When PR #2317 changed the EVM opcode from SHA3 to KECCAK256 it broke the `(sha3 loc len)` expression in LLL. This PR fixes things while allowing existing code using the sha3 expression (such as the ENS registrar) to continue to compile. I.e. both `(keccak256 loc len)` and `(sha3 loc len)` may be used, and the existing related sha3 macros continue to work.
Three end-to-end test cases have been added for kekkac256 and sha3.
test for fallback and fallthrough. Added one test for 'lit'. Added tests
for arithmetic/binary/unary operations. Added the start of tests for
assembler instructions within LLL source.
