Small-C Struct Support

[ZaneDubya]

Add support for structs to the Small-C compiler See here for syntax: https://en.wikipedia.org/wiki/Struct_(C_programming_language)

• [x] Determine struct syntax: definition, declaration, assignment, copying, member access.
• [x] Reserve 'struct' keyword
• [x] Create data structure to hold defined struct types (by name, with reference to members, and total size)
• [x] Create data structure to hold struct members (by name, with type; type can be a struct, allowing nested structs)
• [x] Recognize 'struct' keyword
• [x] Recognize struct layout
• [x] Don't allow initialization in struct def
• [x] Read in struct definitions to defStructs and defSMembers
• [x] Recognize definitions of global structs
• [ ] struct definitions may optionally be followed by variable definitions.
• [ ] later definitions of structs must be preceded by 'struct' keyword.
• [ ] Error out on assignment of struct to number
• [ ] Recognize assignment of global struct (assign all, in brackets)
• [ ] Recognize references to structs
• [ ] Recognize references to struct members
• [ ] Recognize assignment of struct members
• [ ] Recognize partial struct assignment
• [ ] Recognize struct assignment from another struct (deep copy)
• [x] Recognize definitions of local structs
• [ ] Allow passing struct as parameter
• [ ] Allow returning struct from a function
• [x] Allow definitions of arrays of structs
• [x] Allow pointers to structs