Building external plugins against the installed Avogadro


I just added some new CMake code to Avogadro’s build system to
facilitate building plugins against the installed Avogadro library. I
have pushed a new mini project to github to demonstrate how simple an
external plugin can be now,

If you have Avogado installed in any of the normal places this will find
it, set up the build, compile against it and install to the contrib
directory inside the installed prefix by default. This could easily be
overridden by calling commands after it has been installed.

It is still very new, and I think it needs tidying up a little. I do not
think the Find*.cmake files belong in /lib/avogadro/cmake for
example. It also may need some extra logic for Mac and Windows, I have
not tested it there yet. I am hoping to build a fuller example shortly,
but the same approach would work for extension, tool and color plugins too.