TODO

Android version:
* Implement ON / flag 44.
* With some combinations of skins and screens, there are glitches in the
  display -- thin black lines, things being slightly out of alignment.
* Free42 should create /sdcard/Android/data/com.thomasokken.free42/ itself, if
  it doesn't already exist (and use it as the default directory for
  import/export and print-to-file). It can do that, apparently, since I've been
  able to do it using MkDir in Free42's file selection dialog.

iPhone version:
* Make the Xcode build run the version number insertion thing. Apparently,
  build-iphone is a thing of the past, but we still need to update the version
  numbers in release builds somehow.
* Implement ON / flag 44.
* Preferences looks a bit ugly in iOS 7 and later, because the now-much-smaller
  switches no longer line up with the right margin. How do I create a settings
  screen that looks more like the iOS Settings app?
* Add option to disable key click.
* Haptic feedback option.
* Support landscape mode.

Windows version:
* Press a key with the mouse, then move the mouse outside of the window, then
  release the mouse button. The key stays pressed; apparently the mouse-up is
  not handled in this case.
* What would it take to fix the Alt-Tab problem? How do you create a "new"
  style menu bar? This may be relevant: https://msdn.microsoft.com/en-us/library/windows/desktop/hh270423(v=vs.85).aspx

Mac version:
* When you resize the print-out window, the bottom of the print-out shows stuff
  from the top of the print-out, and it keeps doing that until you restart the
  app. Seems like bounding rectangles getting out of sync.
* Modify the file selection dialogs so they have a file type menu, and add
  extensions to file names automagically when appropriate.
* Implement low-battery checker.

Linux version:
* Update low-battery checker to work with /proc/acpi/battery and
  /sys/class/power_supply.

All versions:
* So, you added some code to keep matrices to less than 2 GB in NEWMAT, but
  how about INSROW, COMPLEX, SIZE? Any other opportunities for Bad Things to
  happen with array sizes?
* When a two-line message is active, CATALOG doesn't seem to do anything,
  because the display isn't repainted. (Probably not specific to two-line
  messages?)
* Add a feature for previewing and installing skins from the web.
* Program pasting should accept listings without line numbers.
* Change scalar copy so it only copies full precision in ALL mode.
* Add a feature for importing and exporting variables from and to CSV files.
* Add a feature for importing and exporting programs from and to text files.
* Maybe program pasting should be case-insensitive (except for local labels and
  ALPHA strings, of course)
* Printer emulation: some aspects of TRACE (and probably also NORM) mode
  behavior don't match the original. Two specific cases: the original prints
  feedback when you enter or exit menus ("BASE", "A..F", "EXIT") though not
  always (PRGM mode?); DIM? prints the value returned in X, while Free42 prints
  nothing. I'm sure there are more cases, and I should just check them with
  Emu42 with the HP-82240B emulator.
* Make the printer annunciator linger a bit, so that it is easier (or even just
  possible!) to tell when a program is printing something.
* Make better icons.