Fix install

[ax487]

As was pointed out in #29, the install directories are not set in a fashion consistent with well-established standards:

• Libraries should go into /lib and not in /lib/ColPack_static
• Cmake configurations must go into /lib/cmake/ColPack in order
  for cmake to be able to find them.
• Exported targes should be namespace'd

Also, the includes for the installed files
https://github.com/CSCsw/ColPack/blob/master/build/cmake/CMakeLists.txt#L134-L135
and the location of the installed includes
https://github.com/CSCsw/ColPack/blob/master/build/cmake/CMakeLists.txt#L173
must coincide. Otherwise exporting targets becomes rather pointless.

This request contains fixes to all of these issues. As a result, a simple example project of the form

find_package(ColPack REQUIRED)
target_link_libraries(<example app> ColPack::ColPack_shared)

actually compiles :)