utility : tuple, complex_ops

- add _j notation on C++11 compliant compilers
- correct tuple fold (was working in reverse)
- add construction of mini_vector from tuple
work on gf documentation
work on gf: scalar_valued, ...

- introducing scalar_valued gf
- Change Fourier routines to run on scalar_valued,
and then use those routines to run on matrix_valued.
- Tools for slices of 2 variables functions
draft of multi-time gf (t,tau), etc...
Add details for applis compilation/install

- generation of test script
- export new variables