Replace .version files with a single .shards.info

[waj]

Since #349 every installed shard is accompanied by a .version file with the real installed version. This clutters the lib directory. This PR replaces all those files with a single lib/.shards.info file. This file is also a YAML so the contents could be extended in the future with any required metadata.

[waj]

Note that the previous change is not released yet. So a migration path is unnecessary.

[Sija]

I'd suggest naming the file .shards.yml (or similar but with the .yml extname), since it is an YML file after all.

[waj]

@Sija I think that name could be confused with shard.yml. Also, the shard.lock file is also a yml and yet it has a different extension.

[bcardiff]

@Sija since the two files have different semantics and different schema I don't think is good to name them so similar. .shards.info is fine.

[straight-shoota]

@Sija This is only for internal use and the fact that it's based on a YAML format is an implementation detail. We could decide to change the representation at any point and still keep the same file name.

[straight-shoota]

We could consider naming the file shards.installed or shards.versions to better express the purpose. But I'm fine with shards.info.