Restructing and improve cmake files

  * build RUtil2 as a library(static) actually
  * change the old RUtil2 executable to a unit test case

TODO:
  * add a cmake doc target to generate documentations
  * make the API(header) more user(developer) friendly
Merge branch 'master' of https://github.com/iyzsong/RUtil2 into iyzsong-master
Merge