cursor: How to print cursors

The cursor module is like the print module, in that it provides some basic options on how cursors should be printed. These options primarily concern if cursors should be printed as "real cursors" (The blinking kind, that can turn into a bar and stuff), or as just Forms.

• cursor::set_main will set the "shape" of the main cursor. This takes a CursorShape argument, and lets you set its shape to a vertical bar, a horizontal bar, and make it blink.
• cursor::set_extra is the same but for extra cursors. Do note that this may not work on some Uis, mainly terminals, which only allow for one cursor at a time.
• cursor::unset_main and cursor::unset_extra: Disables cursor shapes for every type of cursor, replacing them with a Form, which will be caret.main and caret.extra, respectively
• cursor::unset: The same as calling unset_main and unset_extra.