Create remind file for Google Calendars.

Take a list of links to Google Calendar iCal files in an input file (for now,
the file must be named "calendar_list" in the same directory).  For each link,
download the file to the /tmp directory, convert it to remind format using the
ruby script ical2rem-cli, and then concatenate it with the previous calendars.
Create remind calendar from all calendar inputs.

Merge the remind calendar from the org files with the remind calendar from
the downloaded Google calendars.  Then, pass this combined calendar to remind
to create the actual calendar printout.

Changed the final calendar's width to 120 characters.