First RESTful HTTP API (#399)

* Added generated code for REST API.
 - Created a new crate rest_api, which will adapt the openapi generated code to Lighthouse
 - Committed automatically generated code from openapi-generator-cli (via docker). Should hopfully not have to modify this at all, and do all changes in the rest_api crate.

* Removed openapi generated code, because it was the rust client, not the rust server.

* Added the correct rust-server code, automatically generated from openapi.

* Added generated code for REST API.
 - Created a new crate rest_api, which will adapt the openapi generated code to Lighthouse
 - Committed automatically generated code from openapi-generator-cli (via docker). Should hopfully not have to modify this at all, and do all changes in the rest_api crate.

* Removed openapi generated code, because it was the rust client, not the rust server.

* Added the correct rust-server code, automatically generated from openapi.

* Included REST API in configuratuion.
 - Started adding the rest_api into the beacon node's dependencies.
 - Set up configuration file for rest_api and integrated into main client config
 - Added CLI flags for REST API.

* Futher work on REST API.
 - Adding the dependencies to rest_api crate
 - Created a skeleton BeaconNodeService, which will handle /node requests.
 - Started the rest_api server definition, with the high level request handling logic.

* Added generated code for REST API.
 - Created a new crate rest_api, which will adapt the openapi generated code to Lighthouse
 - Committed automatically generated code from openapi-generator-cli (via docker). Should hopfully not have to modify this at all, and do all changes in the rest_api crate.

* Removed openapi generated code, because it was the rust client, not the rust server.

* Added the correct rust-server code, automatically generated from openapi.

* Included REST API in configuratuion.
 - Started adding the rest_api into the beacon node's dependencies.
 - Set up configuration file for rest_api and integrated into main client config
 - Added CLI flags for REST API.

* Futher work on REST API.
 - Adding the dependencies to rest_api crate
 - Created a skeleton BeaconNodeService, which will handle /node requests.
 - Started the rest_api server definition, with the high level request handling logic.

* WIP: Restructured REST API to use hyper_router and separate services.

* WIP: Fixing rust for REST API

* WIP: Fixed up many bugs in trying to get router to compile.

* WIP: Got the beacon_node to compile with the REST changes

* Basic API works!
 - Changed CLI flags from rest-api* to api*
 - Fixed port cli flag
 - Tested, works over HTTP

* WIP: Moved things around so that we can get state inside the handlers.

* WIP: Significant API updates.
 - Started writing a macro for getting the handler functions.
 - Added the BeaconChain into the type map, gives stateful access to the beacon state.
 - Created new generic error types (haven't figured out yet), to reduce code duplication.
 - Moved common stuff into lib.rs

* WIP: Factored macros, defined API result and error.
 - did more logging when creating HTTP responses
 - Tried moving stuff into macros, but can't get macros in macros to compile.
 - Pulled out a lot of placeholder code.

* Fixed macros so that things compile.

* Cleaned up code.
 - Removed unused imports
 - Removed comments
 - Addressed all compiler warnings.
 - Ran cargo fmt.

* Removed auto-generated OpenAPI code.

* Addressed Paul's suggestions.
 - Fixed spelling mistake
 - Moved the simple macros into functions, since it doesn't make sense for them to be macros.
 - Removed redundant code & inclusions.

* Removed redundant validate_request function.

* Included graceful shutdown in Hyper server.

* Fixing the dropped exit_signal, which prevented the API from starting.

* Wrapped the exit signal, to get an API shutdown log line.

beacon_node/client/src/lib.rs

@@ -2,6 +2,7 @@ extern crate slog;
 
 mod beacon_chain_types;
 mod config;
+
 pub mod error;
 pub mod notifier;
 
@@ -39,6 +40,8 @@ pub struct Client<T: BeaconChainTypes> {
     pub http_exit_signal: Option<Signal>,
     /// Signal to terminate the slot timer.
     pub slot_timer_exit_signal: Option<Signal>,
+    /// Signal to terminate the API
+    pub api_exit_signal: Option<Signal>,
     /// The clients logger.
     log: slog::Logger,
     /// Marker to pin the beacon chain generics.
@@ -143,6 +146,24 @@ where
             None
         };
 
+        // Start the `rest_api` service
+        let api_exit_signal = if client_config.rest_api.enabled {
+            match rest_api::start_server(
+                &client_config.rest_api,
+                executor,
+                beacon_chain.clone(),
+                &log,
+            ) {
+                Ok(s) => Some(s),
+                Err(e) => {
+                    error!(log, "API service failed to start."; "error" => format!("{:?}",e));
+                    None
+                }
+            }
+        } else {
+            None
+        };
+
         let (slot_timer_exit_signal, exit) = exit_future::signal();
         if let Ok(Some(duration_to_next_slot)) = beacon_chain.slot_clock.duration_to_next_slot() {
             // set up the validator work interval - start at next slot and proceed every slot
@@ -175,6 +196,7 @@ where
             http_exit_signal,
             rpc_exit_signal,
             slot_timer_exit_signal: Some(slot_timer_exit_signal),
+            api_exit_signal,
             log,
             network,
             phantom: PhantomData,