Initial reverb implementation

I'm not sure I understand what you're saying, from what I can tell, this appears to be making a lib from the files you downloaded from the lv2/geverb project. It appears as if you got these files from https://github.com/swh/lv2 and or from http://plugin.org.uk/releases/, and it appears as if you're making a normal staticly linkable library that you're calling from the interface cpp code.

It appears as if the interface/external/gverb/CMakeLists.txt is your own construction to make this library, but it is just an implementation of a cmake based make file for this library.

As far as I can tell, you'd still be able to use the lv2/gverb code pretty much as is if you did the following:

1) Remove the following files: include/ladspa-util.h include/lv2.h src/gverb.h src/gverb.c src/gverbdsp.h src/gverbdsp.c
2) Keep your CMakeLists.txt
3) Change the BUILD.md to include instructions on downloading gverb from the correct sourse (I assume it's from https://github.com/swh/lv2), and set the appropriate environment variables to allow your FindGVerb macro to find the location they checked it out to.