Release 0.9.9 "Headrest" - Ranges

This release introduces four range types to perform computations on ranges, and
fixes serious graphical regressions that remained undetected by the test suite.

New features
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* Three range types, known as _interval_ (`1…3`), _delta range_ (`2±1`) and
  _percent range_ (`2±50%`), for which arithmetic and most operations have been
  implemented.
* An uncertain type (`2±3σ`), for which arithmetic and operations are not
  implemented yet.
* A new flag, `ShowAsDecimal`, presents integers and fractions using a decimal
  format. This is useful for people working in banking, who can use `2 FIX` mode
  for all values. In that mode, `50` will display as `50.00`, and `3/4` will
  display as `0.75`. The `Show` command still shows the original value.
* The simulator now strips CR/LF when pasting on Windows.
* The `^` operator now operates on arrays

Bug fixes
---------

* The image comparison code has been broken since January. As a result,
  various regression regarding graphical output remained undetected.
* One particular case is the generation of incorrect BMP files after the default
  format for graphic objects was switched to `bitmap`.
* A possible crash was eliminated when converting a number to integer, to
  fraction or to decimal.

Improvements
------------

* The `σ` (used for uncertain numbers) replaces `ρ` (unused at the moment) on
  the keyboard in alpha mode.