DRY-up the use of fromHex in the project

Was previously returning nonsensical “0x”

NatSpec integration

* Reimplemented nonce management for known accounts.

* Cleaned up VM execution. VM run now takes a context
* ADDMOD/MULMOD - removed incorrect cast

Allow returning different JSON RPC error codes depending on error type

0749546 random fails
a153865 random fails

git-subtree-dir: tests/files
git-subtree-split: 074954630f43e97f0769997d175511a00a47cc9d

d6c987f go failure

git-subtree-dir: tests/files
git-subtree-split: d6c987feed635976ce26b14b9be88289d0ef50d4

9e19ff9 random state tests failures
7060dc7 dejavu issues
5a89a4b python fail
2470051 python fails - may be just wrong return value

git-subtree-dir: tests/files
git-subtree-split: 9e19ff93918597bbf53a2f127202a70704646d82