Deprecate XK_approxeq and XK_notapproxeq.
It applies the following directives:
For any future extension of the keysyms with characters already found in ISO 10646 / Unicode, the following algorithm shall be used. The new keysym code position will simply be the character's Unicode number plus 0x01000000. The keysym values in the range 0x01000100 to 0x0110ffff are reserved to represent Unicode characters in the range U+0100 to U+10FFFF.
Where the correspondence is either not one-to-one or semantically unclear, the Unicode position and name are enclosed in parentheses. Such legacy keysyms should be considered deprecated and are not recommended for use in future keyboard mappings.
Fixes #20 (closed)