ansi: implement a new ansi.Scanner to replace ansi.Parser

[aymanbagabas]

Currently, the ansi.Parser API is hard to work with and feels flaky. We need a cleaner and Golang idiomatic way to parse sequences and text.

We might need to come up with a container type that can hold the scanned/parsed data to limit allocations. Limiting allocations should be optional, and defaults to unlimited allocations when not specified (or zero is used).

Should we drop the parser sub-package? Replace that with ansi.DecodeSequence? Are there any performance penalties for doing so? How will the new scanner API look like?

Related: #215