Drop hdy_init() and making libhandy static

Having library initialization fucntions is discouraged and should be replaced by library constructors. Unfortunately library constructors don't work with static libraries.

As libhandy has never been designed to be a static library, and having support for it is creating more problems than good (e.g. translations of libhandy are not installeds) and libhandy is already installable to a specific per-project location, I suggest to drop support for building libhandy as a static library to gain consistency and a library constructor.

As this would break the API and drop a build-time feature, I suggest to introduce that with a hard version change like libhandy-0.1.

See !221 (merged).