Add API in compiler for easily calling all native contract methods

[spencercorwin]

Currently users can do this with our linked smart contract API but we could make native contract calls way more user friendly be exposing them directly with something like Native.Ledger.getBlockHash(<index>). This is just an idea. Or maybe we want to expose all those native contract methods in a module like Blockchain.getBlockHash(<index>). Either way all those native contract methods should be exposes very easily to the user in some way.

Make sure to add docs and tests.