Allow Relative Paths

[gunderson]

This pull request adds an option to pass { relative:true } to the path object (either through the object or function methods) in order to keep the path relative to the file glob. Normally this bit is removed and renamed with gulp.dest() but when renaming and concatenating compiled JST template files, the full absolute path name is passed making the name of the template non-portable if developers set up their build environments in different locations.

This small change allows users to pass a flag that eliminates the step of re-applying the absolute path and allows the path to remain relative.

[yocontra]

Sorry for the extremely long wait here. How does this play in with https://github.com/hparra/gulp-rename/issues/67 ?