feat: use StateEither for parser

Three big changes were made in parser.ts. The first is that the parser
is now generic over the stream state type. A basic StringStream has been
implemented but most non-string combinators are generic. The second big
change is that Stream is a mutable interface. The Stream type requires a
take method and an undo method. Take will return some number of inner
values from a buffer and keep a history of all previous cursors. Undo
will back track to the nth cursor. Take only accepts whole numbers, so
the cursor history must monotonically increase. The last big change is
that Parser is implemented over the StateEither monad, which is a new
one for fun.

Some things of note. The standard fail combinator will automatically pop
the last cursor. Since Stream is stateful it is enough to simply create
a fail parser to undo the last take. This makes take/flatmap the primary
combo for creating one off parsers.

Author: baetheus