Updating version for next release

Release will fix problems with setting properties globally and
improve vim integration.
Changed properties to be overridable globally

Changed all the plugin overridable properties to be "in ThisBuild"
in order to allow them to be overridden globally.
Updating files for new features

Updated the readme to reflect that global property overrides now
work. Also added the release notes for 0.3.0.
Changing to use sbt 0.12.4
Fixed a problem with the plugin properties

I prematurely commited and released that last version. Turns out
that several properties were not correctly set in that version.