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)

lighthouse/Cargo.toml

@@ -31,7 +31,7 @@ validator_client = { "path" = "../validator_client" }
 account_manager = { "path" = "../account_manager" }
 clap_utils = { path = "../common/clap_utils" }
 eth2_testnet_config = { path = "../common/eth2_testnet_config" }
-git-version = "0.3.4"
+lighthouse_version = { path = "../common/lighthouse_version" }
 
 [dev-dependencies]
 tempfile = "3.1.0"

lighthouse/src/main.rs

@@ -1,23 +1,15 @@
-#[macro_use]
-extern crate clap;
-
 use beacon_node::ProductionBeaconNode;
 use clap::{App, Arg, ArgMatches};
 use env_logger::{Builder, Env};
 use environment::EnvironmentBuilder;
 use eth2_testnet_config::{Eth2TestnetConfig, DEFAULT_HARDCODED_TESTNET};
-use git_version::git_version;
+use lighthouse_version::VERSION;
 use slog::{crit, info, warn};
 use std::path::PathBuf;
 use std::process::exit;
 use types::EthSpec;
 use validator_client::ProductionValidatorClient;
 
-pub const VERSION: &str = git_version!(
-    args = ["--always", "--dirty=(modified)"],
-    prefix = concat!(crate_version!(), "-"),
-    fallback = crate_version!()
-);
 pub const DEFAULT_DATA_DIR: &str = ".lighthouse";
 pub const ETH2_CONFIG_FILENAME: &str = "eth2-spec.toml";