v0.9.0.rc1 Corpulent Duck

Breaking changes:

• Dependency solver was overhauled, it may resolve dependencies in a
  completely different way, succeed better, or just fail;
• Git tag refs that match a version number are now an actual version (i.e.
  tag: v1.0.0 is converted to version: 1.0.0).

Features:

• Update specified shards only, trying to keep other shards to their locked
  version if possible;
• Add --local argument to use the cache as-is, allowing to skip git fetches
  when you know the cache is up-to-date;
• Add the outdated command to list dependencies that could be updated
  (matching constraints) as well as their latest version; including pre-release
  versions on demand.
• Add the lock command that behaves like the install and update commands
  but that only creates a lockfile, and doesn't install anything.

Fixes:

• Transitive dependencies are now available to all installed shards, allowing
  postinstall scripts to compile any Crystal application;
• Don't consider metadata when considering a pre-release version number.