Allow user to use your official repository with Composer

[seebz]

In order to be known by Composer, you must register your package on the Composer repository.

This allow users to use your official and up-to-date repository instead of forks.

[seebz]

I don't known if git tags was pushed but I suggest tagging versions 0.4.5, 0.5 and 0.5.1

$ git tag 0.4.5 57fb0966b99809c921d959b9483940b2c8095296
$ git tag 0.5 79f61969f63ee77e0d9460bc254a27a671b445f3
$ git tag 0.5.1 dc4785b4d7227fd9905e086d499fb8abfadf9977
$ git push origin --tags

So, users can use Spyc consider as stable by Composer; no more needs to set "minimum-stability" as "dev". (I thinks)

[mustangostang]

Thanks @Seebz, I've merged your pull request, registered Spyc with Packagist and added tags.