FFI

[giann]

FFI implementation. Inside:

• New zdef statement to declare foreign functions and structs in the global scope
• New std lib ffi
• FFI calls are generated with MIR
• Foreign struct getter/setters are generated with MIR
• New Buffer method to handle foreign types:
  • writeZ, writeZAt
  • readZ, readZAt
  • writeStruct, writeStructAt
  • ptr
• object/class collectors #2
• First class types #21
• Allow keywords and non-buzz identifiers as identifiers #138
• Change pattern delimiters #165