SVN style:
  [branch] -Keyword [FS#12345] (r12345): [section] Message. (credits)
  [1.8] -Fix [FS#12345] (r12345): [NewGRF] Everything. (wizzzard)

Discussion:
  - "branch" and "credits" are pointless with non-SVN.
  - Dash: Keep or drop?
  - Keywords kept: 
     -Add, -Feature: Adding new stuff. Difference between "Feature" and "Add" is somewhat subjective. "Feature" for user-point-of-view stuff, "Add" for other.
     -Change: Changing behaviour from user-point-of-view.
     -Remove: Removing something from user-point-of-view.
     -Codechange, -Cleanup: Changes without intentional change of behaviour from user-point-of-view. Difference betweeen "Codechange" and "Cleanup" is somewhat subjective.
     -Fix, -Revert: Fixing stuff.
     -Doc, -Update: Documentation changes, version increments, translator commits.
     -Prepare: Rarely used.
  - Keywords removed:
     -Regression: Regression tests are run during deploying, so pointless.
     -Backport: (Cherry-pick-)merges keep the original messages.
     -Branch, -Release: No such thing with non-SVN.
     -Merge, -Sync: We only do fast-forward merges.
  - Section: Kept as is.
  - Message: First line with "-Keyword", other lines optionally with "-Keyword".
  - Issue link: "-Fix #123:" (alternative could be "-Fix GH-123:"
  - Commit links: "-Fix f2da1eb57c" (using short hash)

GIT style variants:
A: -Fix #123, fix #456, f2da1eb57c, 1f044d3e: [NewGRF] Everything.
B: -Fix #123, fix #456, fix f2da1eb57c, fix 1f044d3e: [NewGRF] Everything.
C: Fix #123, fix #456, f2da1eb57c, 1f044d3e: [NewGRF] Everything.
D: Fix GH-123, fix GH-456, fix f2da1eb57c, fix 1f044d3e: [NewGRF] Everything.