fix: also include 'main' module entry point

This keeps the TypeScript compiler happy as well as the AssemblyScript compiler

fix: make globals static so that they don't pollute downstream librar…

…ies (#42)

Also reorganized top level `let`s into static variables.

fix: repetition nodes were not allowing the walker to visit their chi…

…ld nodes

fix: throw an explicit error when there is nothing to repeat

feat: implemented non-capturing groups

feat: supports multi-line regex

fix: fixed small bug with case insensitive range matching

feat: upgraded to AssemblyScript v0.18

fix: capture groups with quantifiers are not repeated

fixes: 31

fix: harmonise TS and AS execution

ref #17