IMPL: write commits-cache
REFACTOR: split git_parse_commit_line() off

will need it for extending cache
Merge master to dev/commitcache
REFACTOR: nice prototype to retry

say goodbye to top-down source, it's anyway too big
REFACTOR: preparing interface for using commit cache
REFACTOR: move iterate_popen to beginning and make it proper prototype

start making sections
REFACTOR: parse and save at the same time
IMPL PARTIAL: use commits from cache rather than from todo

TODO: resolve missing commits
DOC: make README.md a bit nicer
merge commits-cache
merge testing