Change field execution function generation to use IL emitting

[Horusiath]

Currently during so-called compilation phase we're generating execution function for each field of each GraphQL object - we do it quite naively to be honest. The idea is to replace current function generation mechnism (which uses plain old function cominators + System.Reflection in few places) to function bodies constructed through System.Reflection.Emit.

[xperiandri]

Cool idea! Would you like to help with that?