This is kind of a weird mix of UNIX/Emacs/bash and traditional Atari.

^A - move to start of buffer
^E - move to end of buffer
Shift-Del - delete (clear) buffer
^U - delete to start of buffer.
Shift-Clear or Ctrl-Clear: clear buffer and hide input box (show status)
^W - delete word to left of cursor
Left/Right arrows - move cursor
Backspace - delete the character to the left of the cursor
Ctrl-Del or ^X - delete the character under the cursor
Atari key - insert a ^B (meaning, toggle bold)
^U - delete to start of buffer
^K - kill (delete) to end of buffer.
^F or ctrl-shift-Up - move right by one word.
^B or ctrl-shift-Down - move left by one word.
Tab - Nick completion (only at the start of an empty input box!)
Up arrow - if the inputbox has anything in it, move up 1 line,
   aka 40 characters, or to the start if the text is less than
   40 characters.
Up arrow *in an empty inputbox* - bring up last entered command.
   Can coexist with regular use of Up for movement.
Down arrow - moves down 1 line, aka 40 characters. If this would
   move past the end of the text, moves to the end.
Ctrl-Insert - toggle insert/typeover

Future plans:

^Y, Shift-Insert - paste (^K, ^U, ^W fill a paste buffer; need RAM)
Tab - For [server], complete channels. For [private] and channels,
    complete channel nicks.
Shift-Return: Maybe... send buffer but do not clear it.

The glyphs for these will appear as inverse letters, but will actually
be the appropriate low ASCII characters:
^I - toggle italic
^L - toggle underline
^S - toggle strikethrough