As announced in https://community.gazebosim.org/t/important-gazebo-and-ignition-are-going-to-github/533,
the ignition project repositories have been migrated from BitBucket to GitHub.
This commit updates the ignition_modular_library helpers to use GitHub instead of BitBucket,
and also update the hashes of all the ignition ports as apparently the archive generated by GitHub
for releases are slightly different from the one generated by BitBucket.
* Add ignition-modularscript port
Modeled after the qt5-modularscript port, this port just contain
ignition_modular_library, an helper CMake function to simplify the
process of writing port of C++ libraries developed by the Ignition
Robotics project ( https://ignitionrobotics.org ).
* Add ignition-cmake0 port
* Add ignition-math4 port
