Fix old and new syntax for constant/define/evaluate/variable

[undisbeliever]

This fixes the show-stopper I mentioned in PR #36

Besides the included tests, this PR has been tested against:

• untech-engine (bass-v15 syntax)
• snes-test-roms (bass-v15 syntax)
• 5 samples from https://github.com/PeterLemon/SNES (bass-v14 syntax)