Add MCNAME: an equivalent of MCSTR for NameRefs

Does exactly what it says on the tin.
Replace calls to MCVariable::createwithname_cstring to the StringRef variant

The cratewithname_cstring method has been removed entirely.
Replace MCDeferredVariable::createwithname_cstring method

The new method takes a NameRef instead of a C string.
Merge pull request #223 from runrevfraser/refactor-syntax_unicode_variable

Refactor syntax unicode variable