Problem: PumpkinScript interpreter is inefficient

[yrashk]

Parsing and analyzing PumpkinScript in runtime comes at a cost and can't be nicely optimized by the compiler.

Proposed solution: develop a CPS (Continuation Passing Style) interpreter. The scope of this solution would be rather big, so we can track thoughts/progress/discussions here.

I've started doing some experimental work in a private branch.

HT @5HT