Added support for more brg options (untested)

Support added for update (-u) and package installs (-p) though both are
yet untested. Added warning when specifying -s as there is no specific
repository that is commonly enabled.

-s is not yet implemented in brg, chose $section for it for now.
Added section (-s) option support in brg

-s was listed as an option in the help, but was not accounted for.
Assigned it the environment variable $section, setting it to 1 if
specified.