message: docs: withdraw ccache in makefile
diff: #compile parameters
  # WARN: maybe difficult to install ccache in some systems
  -CC = ccache g++
  -#CC = g++
  +#CC = ccache g++
  +CC = g++
  #the optimazition level of gcc/g++
  #http://blog.csdn.net/hit_090420216/article/details/44900215
  