#793 GTK3V2MAIN: correct documentation syntax issues

[John R. Jackson]

This started out as a pass through the Help documentation to correct spelling errors. Then I
found inconsistencies in the way key presses were presented and started fixing them. Then...

In the end I went through all the docs for a general cleanup:

• fix spelling errors
• for consistency:
  • all unemphasized keys -> \c{<Key>}
  • \[^c]{<Key&gr;} -> \c{<Key&gr;}
  • lots (and lots) of consistency changes in the way keys and key combinations are presented
  • <Space>\c{Ctrl+...}<Space> -> (\c{Ctrl+...}) (when describing a hot key)
  • reduce excessive capitalization
• remove extraneous trailing spaces and (source) blank lines
• condense extraneous repeated spaces
• a few grammatical improvements/corrections (double word, missing word, etc)
• some additional content when it supported cleaning up something else
• fixed XQuartz link to point to the MacInstall Wiki page

I did not:

• change documentation structure (other than adding some bullets)
• make extensive wording changes, although I did try to clean up a few things as I tested

Note: among the spelling changes were:

• colour -> color
• behaviour -> behavior

This was not to annoy my British friends. It was to be consistent and reduce noise from the spell check program.