Add 'git acm' alias

[MrKou47]

compose git add . and git commit command.

[joelparkerhenderson]

Thanks for the pull request!

Generally the short gitalias entries are intended for one command, in a kind of functional style. This is so the commands are friendlier to compose together for novices and also for experts.(And if there's one in the list of short existing aliases that mixes multiple commands, it's probably a good one to remove.)

Spacing and quoting tends to be tricky cross-platform, so I suggest that for your acm alias, it's a good one for your own personal git alias list, rather than the gitalias repo. I do appreciate the work!

Yours:

git acm Add feature foo bar because of lorem ipsum

Existing gitalias that's similar:

git a .
git cm "Add feature foo bar because of lorem ipsum"