Highlight left menu item when a corresponding spec is open

[kshychko]

As now we render a spec as a part of ausdigital.org content, it would be good to highlight a corresponding left menu item, so user will not be confused that he left the current specification section. Please take into account, that specification id (ausdigital-foo) is included into the path to a spec. For example:

http://ausdigital.org/ausdigital-idp/

and

http://ausdigital.org/specs/ausdigital-idp/1.0/

[webilhan]

@kshychko Done

[kshychko]

verified