Fix error in K-10 release notes (already fixed on webpages etc)

Slight update to K-10 release notes.

Handle Unicode on Windows better with new PP.avoid_unicode trace

If the trace variable is true, then the pretty-printer strives to not
print Unicode characters. If it's false, then it obeys the grammar
(which encodes various printing preferences as well). The trace
is initialised to true on Windows systems.

Fix a horrid bug in removing rules from grammars.

Sense of a test was inverted when working over a grammar's binders.

Put release date into release notes.

More formatting tweaks for the release notes.

Minor formatting tweak to release notes.

Remove miniml example, as per hol-developers exchange.

Update release notes to use Kananaskis-10 string.

Also, make title a YAML metadata block to make pandoc generate nice
output.

Next release will be Kananaskis-10 (rename release notes to match)