Conda-forge package

[tony-p]

It would be nice to make behaviortree_cpp conda package so it can be easily included into other projects on multiple platforms, including ROS based projects via the robostack project.

I think conda-forge is the right channel to target given it is ROS agnostic at its core. The ROS bindings could be added to the robostack channels.

Advantages include:

• Easy inclusion including dependency management
• Multi platform
• Prebuilt binary distribution
• Usage in virtual environments

So far to build in a conda environment, the main blocker is the way FindZeroMQ.cmake works. The conda-forge zeromq package includes a shared cmake file, so it isn't actually needed at all, and libzmq can simply be targeted to include.

Other potential improvements are that many of the the included 3rdparty repos are already available as packages on conda-forge (tinyxml2, cpp-sqlite, cppzmq, etc).

In my limited free time at the moment I am happy to try make this happen, although am pretty new to the packaging process, and have already started having a bit of a fight trying to make FindZeroMQ.cmake play nice in the conda environment (just deleting it works, but that obviously breaks all the other builds which is not ideal)