Pirum GH-70: Fix adding multiple dependencies
Pirum GH-71: Catch errors when opening the archive
Pirum GH-69: Link license to URL
Pirum GH-67: Add description to feed
Pirum GH-72: Group dependencies by channel
according to Pirum GH-72, fixed default template
according to Pirum GH-69, fixed default template
according to Pirum GH-69, fixed bartlett template
prepare stable release 2.1.0 synchronized with Pirum 1.1.5