gc: Optimize the local repository to make later operations faster

Usage:
  eg gc

Description:
  Optimizes the local repository; in particular, this command compresses
  file revisions to reduce disk space and increase performance.

  This command is occasionally called during normal git usage, making
  explicit usage of this command unnecessary for many users.  However, the
  automatic calls of this command only do simple and quick optimizations,
  so some users (particularly those with many revisions) may benefit from
  manually invoking this command periodically (such as from nightly or
  weekly cron scripts).

Differences from git gc:
  None.

See also
  Run 'git help gc' for a comprehensive list of options available.
  eg gc is designed to accept the same options as git gc, and
  with the same meanings unless specified otherwise in the above
  "Differences" section.