Add g:templates_global_name_prefix option
Change default global template prefix to work with macs

The colon character causes issues on OSX. '=template=' isn't the
prettiest, but it works, plus the user can change it to something nicer
if they want. Fixes #29
Honor g:templates_global_name_prefix in syntax file autoloading
Merge pull request #1 from John-Appleseed/mac-fix-06-23-2014

Mac fix 06 23 2014