substr is non-standard, and slice handles negative indexes sensibly.
v0.0.8-a: fixed Issue #7, better rules for regex-literal recognition
adds 'two regexes divided by each other' test from Issue #9
Merge pull request #8 from ljharb/use_slice

substr is non-standard, and slice handles negative indexes sensibly.
patch version bump, one additional regex text
tweak to fix logic bug around identifying block labels
v0.0.9-a: fixed bug with regex that has / in it, also changed unterminated regex and string errors into warnings
updated README to explain literalizer more completely
massive perf optimization, mind-blowing :)