add MATHJAX_PATH option for doc; clean install

- MATHJAX_PATH : to select the dir of MathJax
e.g. /Users/ME/MathJax  and so on
- rm the installation of test_diff and injector, which are gone.
- fix dependencies of RST in BuildSphinx so that
the doc depends on the change of RST files

	modified:   doc/CMakeLists.txt
	modified:   doc/developer_manual/conf.py.in
	modified:   doc/user_manual/conf.py.in
	modified:   pytriqs/base/utility/CMakeLists.txt