Move parser routine function pointer to lambda function

[JamesYang007]

Currently, the parser logic uses routine_t = void (*)(const token_t&) which forces compiler to generate functions for every routine even when they can be inlined.

Proposed Solution:

The ideal situation is to create lambda functions (or functors, more generally) for these routines which get passed around. The type routine_t will be defined as std::function<void(const token_t&)>. Most of the existing code can remain.