Prepare v6.7.0
Lazy creation of [GRMustacheConfiguration defaultConfiguration]
GRMustacheContext: faster key lookup
[GRMustache preventNSUndefinedKeyExceptionAttack] is a NOOP
GRMustacheRenderNSFastEnumeration now stops enumerating as soon as an error occurs
Slight refactoring of rendering object for nil
Slight refactoring of the storage of a tag's type
[GRMustache escapeHTML:] optimization: don't create autoreleased objects unless necessary