Support Erlang Guard expressions

[michallepicki]

I think it would be great if at least some of the Guard Expressions could be used in Sesterl pattern match clauses. I would very much welcome mainly arithmetic, boolean, short-circuting expressions and comparisons.

It probably doesn't make much sense to support type guards (maybe code generator could insert them some day when concrete types are present if it proves beneficial to performance in benchmarks thanks to Erlang JIT's future type-guided optimizations, there aren't that many of them yet).