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
This class extends the basic ZMQ addresses with addresses that handle
parsing and generating of addresses with embedded curve pubkeys of
various forms, along with a QR-friendly address generator.