Add .gitattributes to make the package lighter when deploying for production.

Running ```composer install --prefer-dist``` will exclude any files and directories specified within .gitattributes.
Update notes in README, example link was broken.

example.php doesn't exist anymore.
allow taxonomies to be sorted with sortable method
Add .gitattributes to make package lighter when deploying for production.

Merge branch 'composer' of git://github.com/vinkla/wp-custom-post-type-class into v1.2.0-rc1
Update notes in README, example link was broken
update changelog
bump version
Merge branch 'refs/heads/v1.2.0-rc1'