Arch dependent paths

[richmattes]

It looks like #26 updated the code to install the cmake module configs to arch dependent paths based on checks that the cmake package version script is making.

The problem is that urdfdom-headers really is architecture independent, and making it architecture dependent doesn't really buy you anything. It just makes it harder to package.

I think the better solution would have been to disable the architecture check instead of updating the install path. The documentation recommends using custom confg-version.pc.in instead of using the helpers if the version checks should be altered. It also looks like you can work around the version checks in the default templates by adding set(CMAKE_SIZEOF_VOID_P "") to CMakeLists.txt. That seems to work in my testing, but it's a little bit hacky.

I filed a bug against cmake to add an option to disable the architecture check, but any changes there won't help in the near term

Also, the pkg-config file is being installed to lib/pkgconfig. It's also architecture independent, so it should be going to share/pkgconfig.

[scpeters]

cc @j-rivero