etc: added quota related settings
quota: reduce parallelism in tests to make them more reliable

Related to #382.
quota: added Set function

This function redefines the quota of a user.

Related to #382.
quota: added example for the Set function

Related to #382.
quota: fix typo in Set docs

Related to #382.
quota: rename user to owner

"owner" is more generic, expressing better the intent of the package.

Related to #382.
quota: fix bug in the limit comparation

My bad x)

Related to #382.