cmake build (wip)

* cmake build file builds libsodium and tests (if requested) and also creates install targets
* removed manually-created visual studio solution and project files
* generate resource.rc on win32 platforms and build it into the DLL
* added ctest support
* added cpack support

Tests are build by default, to disable building tests use `cmake -DBUILD_LIBSODIUM_TESTS=off ..`. 

The simplified build output is forcing the build outputs to be in `bin` and `lib` on visual studio generators.

I do not have the chance to test it on OSX.

Tested with generators
- [x] Visual Studio 12 (win32)
- [x] Visual Studio 11 (win32)
- [x] Unix Makefiles (Cygwin)
- [x] MSYS (win32 not cygwin)
- [x] Unix Makefiles (Linux)
- [ ] MinGW (Linux cross compiling)