Merge branch 'refactor-syntax_unicode' into refactor-syntax_unicode_graphic

Requires updated libfoundation/foundation.h header from upstream in order to clean up some StringRef/DataRef conversion code.
Simplify the new IO_{read,write}stringref functions

The implementation of these methods is much simpler, making use of the MCStringEncode and MCStringCreateWithBytesAndRelease functions.
Simplify MCGraphic::{Get,Set}UnicodeLabel

These methods now use the new MCString{Encode,Decode}{,AndRelease} functions, making their implementations much simpler.
Add Unicode support to MCField

MCField now uses an MCStringRef to store its label.
Simplify MCField label handling

As per Mark's suggestions, simplified the label handling for MCField (the label should now never be set to nil, only the empty string).
Simplify MCGraphic::SetLabel

SetLabel was more complicated that necessary; the input parameter can never be nil.
Removed un-necessary checks for nil
Merge pull request #153 from runrevfraser/refactor-syntax_unicode_field_clean

Refactor syntax unicode field clean
Further cleanup

Cleaning up some minor bits and pieces that got missed previously.
Merge pull request #150 from runrevfraser/refactor-syntax_unicode_graphic

Refactor syntax unicode graphic
Merge branch 'refactor-syntax_unicode' into refactor-syntax_unicode_object