[Grammar] Types

[AtomCrafty]

Implements suggestions 10, 11, and 12 from #39 and fixes #23.

Structure Changes

• User types can no longer be defined within a type specifier
  • They are instead declared within the architectural_state section
  • 6 relevant classes: {Struct|Union|Enum}TypeSpecifier pointing to {Struct|Union|Enum}TypeDeclaration
• Simplified function declaration grammar
  • It is now syntactically valid to specify extern on a function with body, or omit the body of a non-extern function
  • Attributes are now valid on extern functions
• Removed support for designated initializers

Name Changes

Old Class	Old Field	New Class	New Field
CoreDef	contributingType	CoreDef	providedInstructionSets
FunctionDefinition	type	FunctionDefinition	returnType
ExpressionInitializer	expr	ExpressionInitializer	value
BitField	left	BitField	startIndex
BitField	right	BitField	endIndex
Field		EncodingField