Option for custom id transforms.

[sullivanpt]

A custom id mapping can be provided. Examples: // do not trim the whitespace from the string ends (the current default) catalog.setIdTransform(fn(s) { return s; }) // apply html whitespace trimming rules catalog.setIdTransform(fn(s) { return s.replace(/\s+/g,' '); })

I am also submitting a matching pull request for rubenv/angular-gettext-tools References rubenv/grunt-angular-gettext#1, rubenv/angular-gettext#183