Set use-simple true for git
Conditional load functions (vcs_info, is-at-least, add-zsh-hook)
Fix a bug: error occurs if the merge branch is not exists
Remove spaces after sigils
Change colors.

Bold yellow did not work with my solarized theme.  Change it to blue to
match rest of prompt.
Merge branch 'master' of https://github.com/expez/zsh-vcs-prompt