Fix broken installation of headers.
Fix broken installation of headers.

I introduced wrongly installed header paths in my earlier commit
that added the header files to the examples dependency for better
IDE integration. Didn't adapt the paths for install() accordingly
so it broke when trying to install.

alanpich/AutobahnCpp,tavendo/AutobahnCpp,alanpich/AutobahnCpp,e12009/AutobahnCpp,stopthatcow/AutobahnCpp,tavendo/AutobahnCpp,alanpich/AutobahnCpp,stopthatcow/AutobahnCpp,jpetso/AutobahnCpp,jpetso/AutobahnCpp,e12009/AutobahnCpp,jpetso/AutobahnCpp