Link references to complex search specs to the documentation for them
Don't use the word "simple" when describing complex search specs

The rest of the documentation uses the words "complex" or "non-simple"
to describe these search specs and exclusively uses "simple" to describe
the non-complex searches.  It's confusing to describe search specs as
both "non-simple" and then talk about "simple" non-simple search specs.
Merge pull request #13 from CPAN-API/tsibley/search-spec-clarification

Clarify search spec documentation