0.8.3

This is primarily a bug fix release.  Changes include:

- pixel buffer api cleanups
- entry ask question fixes
- ability to access configuration from script plugins
- fix parsing of plymouth:debug and plymouth:splash on kernel cmdline
- build fixes
- export config dirs through pkgconfig
- improve robustness of event loop
- lock other programs out of mucking with tty while plymouth is running
- fix small race when vt switching on quit
- fixes to throbber control
- always set progress to 100% before quitting splashes
- improve boot time estimation heuristics
- add new features to two-step plugin
- queue messages for later replay