Merge branch 'ah/git-prompt-portability'

The command line prompt support used to be littered with bash-isms, which has been corrected to work with more shells. * ah/git-prompt-portability: git-prompt: support custom 0-width PS1 markers git-prompt: ta-da! document usage in other shells git-prompt: don't use shell $'...' git-prompt: add some missing quotes git-prompt: replace [[...]] with standard code git-prompt: don't use shell arrays git-prompt: fix uninitialized variable git-prompt: use here-doc instead of here-string