The previous macro used the set built-in in a way incompatible with the current
implementation of set. This commit updates the macro to be more transparent in how it's
working and avoids the use of the set and alloc built-ins.
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.
