Merging CMAKE changes

[Cazadorro]

@wjwwood Is it possible to have this merged? Our team currently relies on this change to even use this library, since we don't use Catkin at all. With out this we essentially have to maintain our own fork of this library until you do.

[wjwwood]

I'm not planning on merging that, sorry. I would recommend you maintain your own fork for now.

There have been numerous similar pull requests/issues in the past. I will be moving away from catkin in the future, but I'll do that in the next major release. I don't know when I'll get to it, but I'll probably roll my own set of changes for updating to pure CMake.

[wjwwood]

I appreciate you opening the pull request though (even if you close it after my update), it might be useful to others in the meantime.