(try to) Improve the user Manual
(try to) Improve the user Manual

- split install section intro "prerequisite" and "installation"
- specify that gcc>=4.7 is required

artas360/pythran,pbrunet/pythran,pombredanne/pythran,pombredanne/pythran,serge-sans-paille/pythran,pbrunet/pythran,serge-sans-paille/pythran,pbrunet/pythran,pombredanne/pythran,hainm/pythran,hainm/pythran,artas360/pythran,artas360/pythran,hainm/pythran