user-doc: extract, added suggestion by Janos to have
the double dash instead of the long one
Stopped double hyphens being turned into long dashes in manual
Merge branch 'v2.1' of https://github.com/plumed/plumed2 into v2.1
Made compilation less noisy

To have the noisy behavior just compile with
make VERBOSE=1
Shorter dev doc
Added script to push doc from travis

I fixed changlog CHANGES/v2.0.txt since it was not properly
showing (probably doxygen 1.8.6 could interpret it correctly)

[makedoc]
Merge branch 'v2.1'

[makedoc]