Previously you could only generate a string from a string_view, or could
manage the string yourself and pass input iterators plus an output
iterator.
This commit adds an intermediate version that creates a string from a
pair of input iterators.
Removes lokimq::string_view (the type alias is still provided for
backwards compat, but now is always std::string_view).
Bump version (on dev branch) to 1.2.0