"git vendor -h" produces an unhelpful message:

  $ git vendor -h
  usage: git vendor

Move some code so a proper usage message will be issued.

Note that "git vendor --help" is processed by the "git" binary (not
"git-vendor") and thus is unaffected by this change.

support ssh repos

support repositories with SHH URL.
e.g. given repository URL `ssh://git@some.domain.com:7999/project/cool-stuff.git`
before the change the resulting directory will be: `vendor/git@some.domain.com/7999/project/cool-stuff`
the directory after this change will be: `                 `vendor/some.domain.com/project/cool-stuff``

Fix bashisms.

I have a feeling this script was created on OSX because then it would be
being executed using on old bash in strict mode. On Ubuntu 14.04 though
it's executed using dash and various parts fall over because there's a
bunch of bash-specific code in here.

I corrected the problems that the checkbashisms script reported and it
seems to be working better now.

- Use printf instead of echo where escapes are necessary.
- Don't use double bracketed if statements where unnecessary.
- Use -o instead of ||

Fix issue not listing all dependencies

fixes #4

Add git-vendor remove and cleanup some code