Fix error propagation in `Parser.get`.
Change the order of arguments to `parse_*` functions to be more natural.
Introduce a `map` combinator.
Introduce an `ignore` combinator.
Rename `optional` to `option`.
Fix construction of the result list in `many`.
Add `skip` and `skip_many` combinators.
Make error message in `any_char` more precise.
Add `satisfy` character parser.
Implement `char` in terms of `satisfy`.
Add `one_of` and `none_of` character parsers.
Add `space` and `spaces` character parsers.
Clean up the `string` implementation.

* Use `any_char` to parse characters.
* Measure codepoints, not byte size.
Use "character" instead of "codepoint" in error messages.