Add WebKit UA variables
Support toggling user variables

User variables are all strings, so the integer logic doesn't get run.
Instead, if the value is "0" or "1" and no arguments have been given,
toggle between them. This is not done for builtin variables since
anything which makes sense to toggle is an integer.
Add manpages from Debian
Install python files to DESTDIR as well
Merge branch 'dev/fix-python-install' into mathstuf/next

* dev/fix-python-install:
  Install python files to DESTDIR as well
Merge branch 'dev/add-man-pages' into mathstuf/next

* dev/add-man-pages:
  Add manpages from Debian
Merge branch 'mathstuf/dev/cleanup' into mathstuf/next

* mathstuf/dev/cleanup:
  Support toggling user variables
  Add WebKit UA variables