fix(#77): Make query parser more c++-friendly

Update ZealSearchQuery to process no semicolons but first
and to not consider several semicolons at the beginning
as docset filter separator.

Was:

    c++:std::string => docset=c++ query=std
    std::string     => docset=std query=

Now:

    c++:std::string => docset=c++ query=std::string
    std::string     => docset=    query=std::string

See https://github.com/jkozera/zeal/issues/77