Add CMake Integration

[cthbleachbit]

Current build system is somewhat cumbersome for distro packaging. I have devised CMake support, which provides a few more options:

• Default to build the library as a shared object with proper versioning
• Option to build the library as a static object, i.e. an a file
• pkgconfig support
• Option to skip tests and demo from the build
• Follow GNU standard installation locations

[cthbleachbit]

This should make life easier for distro maintainers as is described in #8. You should now be able to build and install locally to /usr/local, where pkgconfig will take care of integrating config4cpp into other projects.