Implements character sets

[mildsunrise]

Changes:

• [X] Make TermState keep track of each character set (G0, G1, G2, G3) independently, and the active one.
• [X] Implement SI and SO.
• [X] Implement ESC N O n o.
• [X] Implement ESC ( ) * + - . correctly (also fix parsing in rare cases).
• [X] Fix parsing of ESC % C, which didn't consume the extra character.
• [X] Parse ESC / C, which designates G3.

The this._modes.graphic attribute is still updated for backwards compatibility.

Without this, some implementations of ncurses behave incorrectly when $TERM = screen because they set G1 to graphics (\e)0) and after some time perform a SO to select it (\x0E). Note that the distinction between GL / GR is not implemented yet.

[mildsunrise]

Thanks for landing this at v1.0.9!

[Gottox]

You're welcome! Thanks for using terminal.js 😄