AST compressing

[thautwarm]

Generated functions(EDIT: in GG) encode the programs into types, in this way the world age problem got solved.

However, the encoded types finally become too large and crash the compiler: #46

An alternative solution is reducing the encoded types but keeping the information.

So far no idea of this approach but just now chatting with some one inspired me and I now thought this deserves some research.

A straightforwaed idea is constructing a bi mapping from a Julia AST to a flatten byte sequence, and the latter can be used as a value type.

[thautwarm]

If this works, #46 can get resolved.