add new scripts: catkin_generate_changelog and catkin_tag_changelog, pulled in function bump_version from catkin
allow mixed state in repository when running catkin_generate_changelog
add GitHub auto linking for issues in catkin_generate_changelog
[catkin_generate_changelog] add option to output the repository wide information to the console
Merge pull request #44 from ros-infrastructure/changelog-generation

add new scripts: catkin_generate_changelog and catkin_tag_changelog