Lighthouse v0.2.0 (Medalla) (#1452)

## Issue Addressed

NA

## Proposed Changes

- Moves the git-based versioning we were doing into the `lighthouse_version` crate in `common`.
- Removes the `beacon_node/version` crate, replacing it with `lighthouse_version`.
- Bumps the version to `v0.2.0`.

## Additional Info

There are now two types of version string:

1. `const VERSION: &str = Lighthouse/v0.2.0-1419501f2+`
1. `version_with_platform() = Lighthouse/v0.2.0-1419501f2+/x86_64-linux`

(1) is handy cause it's a `const` and shorter. (2) has platform info so it's more useful. Note that the plus-sign (`+`) indicates the the git commit is dirty (it used to be `(modified)` but I had to shorten it to fit into graffiti).

These version strings are now included on:

- `lighthouse --version`
- `lcli --version`
- `curl localhost:5052/node/version`
- p2p messages when we communicate our version

You can update the version by changing this constant (version is not related to a `Cargo.toml`):

b9ad7102d5/common/lighthouse_version/src/lib.rs (L4-L15)

beacon_node/eth2_libp2p/Cargo.toml

@@ -14,7 +14,7 @@ serde_derive = "1.0.110"
 eth2_ssz = "0.1.2"
 eth2_ssz_derive = "0.1.0"
 slog = { version = "2.5.2", features = ["max_level_trace"] }
-version = { path = "../version" }
+lighthouse_version = { path = "../../common/lighthouse_version" }
 tokio = { version = "0.2.21", features = ["time", "macros"] }
 futures = "0.3.5"
 error-chain = "0.12.2"

beacon_node/eth2_libp2p/src/behaviour/mod.rs

@@ -77,7 +77,7 @@ impl<TSpec: EthSpec> Behaviour<TSpec> {
 
         let identify = Identify::new(
             "lighthouse/libp2p".into(),
-            version::version(),
+            lighthouse_version::version_with_platform(),
             local_key.public(),
         );
 

beacon_node/eth2_libp2p/src/config.rs

@@ -131,7 +131,7 @@ impl Default for Config {
             discv5_config,
             boot_nodes: vec![],
             libp2p_nodes: vec![],
-            client_version: version::version(),
+            client_version: lighthouse_version::version_with_platform(),
             disable_discovery: false,
             topics,
         }