Basic match for integers; bugfix

[AdUhTkJm]

Adds support to match expression on integers.

Currently, if we denote the set of values to match against as S, only those cases subject to max(S) - min(S) <= 20 will be compiled.

For larger ranges (such as the one in match03), I plan to implement an algorithm of finding a perfect hash function that hashes them into [0, len(S)), so they can fit in a jump table. (On the contrary, the WASM backend just compiles it into a series of if-else.) For len(S) <= 3, I also plan to compile them into if-else.

Bugfix:

• match on variants now works with Cexpr_join_apply.
• escape analysis now works properly; it should be done with backwards data flow approach, not forward.