[CMake] configure resources dir using PLUG_RESOURCES_DIR variable

[yatskevich]

2 changes in this PR:

1. Ability to configure resources dir using PLUG_RESOURCES_DIR variable

This can be handy when a project has a layout like this:

<root>
|- CMakeLists.txt
|- iPlug2
\- YourProject
   |- resources
   |- installer
   |- scripts
   |- etc...

PLUG_RESOURCES_DIR in CMakeLists.txt can be set to:

set(PROJECT_DIR "${CMAKE_SOURCE_DIR}/YourProject")
set(PLUG_RESOURCES_DIR "${PROJECT_DIR}/resources")

If a user doesn't specify PLUG_RESOURCES_DIR, it'll be initialized to ${CMAKE_SOURCE_DIR}/resources.

2. create 'plugin_build_dir' at build system generation time
It seems that this change has been lost in the process of transferring changes from #923

[olilarkin]

thanks for the PR. It's good if you can make a PR for each thing in future.

I don't understand 2. On my mac I just get an empty folder "out" in the build directory

[yatskevich]

Yep, sure – next time every piece of functionality will be in its own PR. I've included 'plugin_build_dir' commit just because I thought it was unintentionally skipped :)

Regarding plugin_build_dir – this directory is being used in postbuild-win.bat.in. If this directory is missing – the postbuild-win.bat will fail. It might be that creating an out dir in postbuild-win.bat is a better option, but I've decided not to change the script.

[olilarkin]

I'm not totally happy with the structure & MSVC projects that the cmake build scripts are making at the moment so I will improve this and maybe edit the script if needed

[yatskevich]

Let's discuss it! I'm ready to help with improvements.