Added m-{a-z} and '-{a-z} commands (#57).

These commands allow to set or jump to marked place of the current opened
page.
Allow to toggle between two locations with '' (#57).
Merge branch 'feature/marks'
Evaluate 'no_proxy' environment variable (#49).

If the no_proxy environment is found and vimb is compiled with libsoup>=2.42.2
this list of domains or ips is bypassed from proxy.