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 in A parser for DEC’s ANSI-compatible video terminals, 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.