A short excerpt from the gitchangelog documentation about how to format the commit messages:

Format

  ACTION: [AUDIENCE:] COMMIT_MSG [!TAG ...]

Description

  ACTION is one of 'chg', 'fix', 'new'

      Is WHAT the change is about.

      'chg' is for refactor, small improvement, cosmetic changes...
      'fix' is for bug fixes
      'new' is for new features, big improvement

  AUDIENCE is optional and one of 'dev', 'usr', 'pkg', 'test', 'doc'

      Is WHO is concerned by the change.

      'dev'  is for developpers (API changes, refactors...)
      'usr'  is for final users (UI changes)
      'pkg'  is for packagers   (packaging changes)
      'test' is for testers     (test only related changes)
      'doc'  is for doc guys    (doc only changes)

  COMMIT_MSG is ... well ... the commit message itself.

  TAGs are additionnal adjective as 'refactor' 'minor' 'cosmetic'

      They are preceded with a '!' or a '@' (prefer the former, as the
      latter is wrongly interpreted in github.) Commonly used tags are:

      'refactor' is obviously for refactoring code only
      'minor' is for a very meaningless change (a typo, adding a comment)
      'cosmetic' is for cosmetic driven change (re-indentation, 80-col...)
      'wip' is for partial functionality but complete subfunctionality.

Example:

  new: usr: support of bazaar implemented
  chg: re-indentend some lines !cosmetic
  new: dev: updated code to be compatible with last version of killer lib.
  fix: pkg: updated year of licence coverage.
  new: test: added a bunch of test around user usability of feature X.
  fix: typo in spelling my name in comment. !minor

  Please note that multi-line commit message are supported, and only the
  first line will be considered as the "summary" of the commit message. So
  tags, and other rules only applies to the summary.  The body of the commit
  message will be displayed in the changelog without reformatting.