[merge request] Viewport doc, module rename, etc.

[Teika Kazura <teika lavabit com>]

Hi. Please merge my branch. It contains:

* Viewport doc improvments. 'viewport-offset' is renamed to 
  'viewport-offset-pixel'. 'window-absolute-position' docstring bugfix.
* wm/commands/user.jl is renamed to launcher.jl. Commands 'xterm' and
  'browser' can take an arg from configurator. Doc.
* 'uniconify-to-current-viewport' was deprecated, but is valid again.

Regards,
Teika (Teika kazura)