Feature Request: add micrate executable when micrate shard is installed

[a-alhusaini]

I think micrate should be added to ./bin as an executable when the shard is installed.

This can be achieved by appending the following to shard.yml

scripts:
  postinstall: shards build

executables:
  - micrate

Thanks to @Blacksmoke16 for providing the above code sample.

[drujensen]

@appdevland Can you create a PR?