CMakeLists: Auto-Parallel

- libSplash and tests detect automatically, if a parallel build is possible
- MESSAGE's use the flag STATUS now. That avoids blowing up the ccmake
  GUI while editing flags
- travis: less flags required
Update doc: no -DPARALLEL=ON required
Merge pull request #18 from ax3l/topic/CmakeParallel

Topic/cmake parallel - Close #17