TODO:
- Macros
- Configurable colors
- Undo
- Keybindings (+ provide a precooked EMACS-mode or mcedit-mode)
- Inputline history and tab-completion
- More flexible exmode - support mixing short commands and giving arguments
  to commands directly at the exmode line
- More flexible presentation layer: like placing a <br> at a given file point
  and having record size larger than column width (== placing <br> at regular
  intervals)
- Bit-unpacking? Show files on less than byte level, useful e.g. for fonts
  or naive bitmaps
- Compression/decompression support
- Support for adding extra space every N columns
- Prefill current filename for :r and :w

Expressions TODO:
- = operator (left side must be a register)
- Mark registers ("'m containing mark offset)
- Do something reasonable about endianity (make it possible to flip it at
  runtime, too, perhaps even inside expressions with a modifier - ':'
  operator?)
- Make statusbar an expression

Code FIXME:
- Perhaps we should merge the basic input key processing in
  fileshow and uimain.
- strtoll() nonportable usage.
- Large regions aren't supported well (they _are_ per se but
  loading/saving/yanking/deleting/... really isn't)
- Search is optimized only for constant expressions, some more work
  is needed here
