Virtual terminal state machine implementation.
This library provides the lowest-level handling of a virtual terminal stream,
recognizing escape sequences and other control characters and delivering
them to a caller-provided handler.
For example, given the sequence `"\x1b[10;10H"` this library can report that
this is a control sequence with function character `H` and the parameters
`[10, 10]`, but it's up to the provided handler to interpret that as a command
to move the cursor to row 10, column 10.
As with so many libraries like this, the state machine is based on the
work of [Paul Flo Williams](https://hisdeedsaredust.com/) in
[A parser for DEC’s ANSI-compatible video terminals](https://vt100.net/emu/dec_ansi_parser),
though any flaws are mine. This implementation does not aim to be fully
compatible with VT100 or its successors. In particular, it implements a
Unicode-native machine that does not support legacy character sets.