Ros-get

-------------------
- Fix tests. [Rein Appeldoorn]
- Feat: --rosdep-check-install. [Rein Appeldoorn]

Only verify the `rosdep` dependencies instead of downloading and
installing them.
- Update README.rst. [Rein Appeldoorn]

-------------------
- Switch to github actions CI. [Ramon Wijnands]
- Automatically determine which build tool to use. [Ramon Wijnands]
- Add fallback behavior colcon on Python2. [Ramon Wijnands]
- Add missing colcon dependency. [Ramon Wijnands]
- Add --colcon argument to support ROS2 workspaces. [Ramon Wijnands]
- Update setup.bash snippet for install space usage. [Ramon Wijnands]
- Add check for existence of directory in ws-list. [Ramon Wijnands]

-------------------
- Add python version to the --version print. [Ramon Wijnands]

-------------------
- Fix 93: AttributeError: 'Namespace' object has no attribute
'ros_distro' [Ramon Wijnands]

-------------------
- Add description for matrix include. [Ramon Wijnands]
- Use unittest.mock on Python 3. [Ramon Wijnands]
- Pin mock at version 3 on Python 2, fix 91. [Ramon Wijnands]

Mock v4 is not compatible with Python 2. Unfortunately the pip version
on 16.04 is too old to install the correct version.
- Update travis to xential & bionic. [Ramon Wijnands]
- Add test for running ros-get without arguments. [Ramon Wijnands]
- Fix running ros-get with no arguments (python3) [Ramon Wijnands]
- Reorganize argument parsing code to allow for testing. [Ramon
Wijnands]
- Add pip install guide to README, fix 87. [Ramon Wijnands]
- Update changelog. [Ramon Wijnands]

-------------------
- Feat(update): Added --restore-versions option. [Rein Appeldoorn]

Closes https://github.com/Rayman/ros-get/issues/85