Parsing for TypeClassLang

[hrutvik]

Redirect parsing to target TypeClassLang

Aside from PureLang's existing constructs, this will need to handle:

• class and instance declarations
• contexts/type class constraints in types
• TypeClassLang's new top-level program structure
• pattern guards
• type annotations at the expression-level

[Gordon-Sau]

Class and Instance declarations are included in the AST, and the types are expanded with constraints. There are incremental updates in the parser.

Design Decision

• It is decided that the parser should raise errors when a top level type signature is found inside Instance block