Also make possible to retrieve the artifact when searching for matches
between repositories list. This made possible to show the package list
when calling `luet search`.
* cmd/search: Add support for search of the packages
with a specific label.
* review Search method of Repositories for permit
different search modes.
* labels are k/v attributes and could be matched
through label key (with HasLabel method) or through
regex that use "$key" + "=" + "$value"
The version inmemory is optimized, while the boltdb implementation is
not.
It returns a list of the same package but with all the versions present
in the db.
Unmarshalling needs well-defined structs, also swap pointers in few places where needed.
There are few more TODOS pending (like getting UpdatePackage fixed properly)
Split dependency resolving ( definition <-> db mapping ) into a method of the tree (ResolveDeps),
and do not care of looking up for packages while parsing.
Note: it is slower but it is much accurate and we can
choose what to do with the ones which aren't resolved (and show a helpful message too).
