Change license to GPLv2+

The Linux kernel is licensed under GPLv2. As GPLv3 and GPLv2 are incompatible in
some way, just license bbswitch as GPL 2.0 or (at your choice) any latter
version. Note: I wrote all code of bbswith.c, so I am entitled to change the
license and do not need permission from other authors (as there are not any).

Request made by Ludwig Nussel.
Clarify why Buffer is used instead of Package
README.md: Fix Markdown
Merge pull request #71 from TimothyGu/master

README.md: fix indentation of upstart script for enabling graphics on shutdown
Linux 3.13 compatibility

Reported by ArchangeGabriel, original patch by tuxoko (Issue
Bumblebee-Project/bbswitch#75)
Update to version 0.8, update NEWS