better installation directories

PR #27 minus the whitespace.

Ping @AndrewBurns.

Much easier to read.

So, I presume that including GNUInstallDirs sets the variable values for CMAKE_INSTALL_LIBDIR and the like. Does this work independent of the compiler? We also want this to function with intel and other compilers.

The directories only depend on the operating system, not the compiler; see here.

Okay, after looking through it, this looks good. Unless @demarle or @joseph.g.hennessey2.ctr have any objections I will merge it in this either Thursday or Friday.

merged

mentioned in commit 009e6e18