Add .mailmap file.

The mailmap is used by git-shortlog(1), git-blame(1) and others to
translate incorrect committer names into unique names for each author.

Use git shortlog -sne to get a commit count for each author after
mapping using the mailmap.
Add line count script.

Uses git-blame(1) and some shell code to count how many lines of code
are blamed on each author.
Add _clang-format file.