Completed translation of '03 Aggregation Pipeline' into Spanish. Close #278.
Minor edits for #278.
Translated
Merge pull request #300 from puentesarrin/issue-278

Completed translation of '03 Aggregation Pipeline' into Spanish.
Merge pull request #305 from jcarlosgarcia/using-max-min

Completed translation of "12-Using_$max_and_$min" parts a and b. Resolves #296