Merge pull request #226 from paulsowden/master

[core] Guard against state.getItemCount() being < 0

[travis] Update to use build tools 21.1.2

[build] Update to latest gradle and android plugin

Merge pull request #168 from blazmag/master

[readme] Add note for ProGuard users

[readme] Upload stable release version

[core, layouts] Add empty application tag to workaround a Gradle bug

[layouts] Don't apply adapter constraints when restoring items

[layouts] Fix NPE when restoring ListLayoutManager state

[readme] Update stable release version

[layouts] Remove the now unnecessary resetLayoutState() method

[core, layouts] Re-implement first-visible child handling

[core, layouts] Re-do update handing and implement lane invalidation

[core] Add getAdapter() protected method to TwoWayLayoutManager