Update $Command global variable where needed
Refactor query_changes routine

Now it receives a list of options after the list of queries. This is
more flexible because the caller can decide which options should be
passed to Gerrit.
Reformat output of subcommand 'query'

Previously, the query subcommand generated a table with the following
columns:

    ID STATUS CR UPDATED PROJECT BRANCH OWNER SUBJECT

Now, the columns are these:

    ID BRANCH STATUS SUBJECT OWNER CR

The UPDATED timestamp was taking too much space for very little
information, considering that the changes are already sorted by last
UPDATED time.

The PROJECT also wasn't conveying nothing because all changes shown were
from the same project anyways.
Do not show recently closed changes by default

The 'git my changes' command used to show a list of recently closed
changes, similar to what Gerrit's web interface does. However, these
changes came together with the 'outgoing' and 'incoming' reviews, which
are much more important usually. Hence, the 'git my changes' command
doesn't show recently close changes anymore. To see them you may use the
'git my closed' command instead.
Implement 'git my closed'

This new argument to the 'git my' subcommand shows the recently closed
changes, which were previously shown in 'git my changes'.
Document all 'git my' arguments