Permit interpolation with or without one-space padding.

In other words, both "{{ foo }}" and "{{foo}}" will be permitted.
AngularJS allows both forms, and there does not seem to be an
established idiom. Also removed unused `start` and `end` vars from
clang.directive.interpolate namespace.
Merge pull request #13 from amacdougall/master

Permit interpolation with or without one-space padding.