Updated installation-instructions and fixed Doxygen-file

installation-instructions:
 - updated use of Homebrew instead of fink
 - added XCode command-line-tool dependency
 - separated the usage-examples of fracture
 - improved instructions for OSX 10.9.4

Doxygen-file:
 - added -directory
 - added REAMDE.md as mainpage
Merge pull request #40 from gismo141/master

Updated installation-instructions and fixed Doxygen-file

Thanks gismo141!