bin/xbps-query: improve argument parsing

[classabbyamp]

makes the behaviour of the -R/--repository flags match what xbps-install et al. do, namely -R <repo> and --repository <repo> now work. Existing behaviours are preserved.

allows PKG argument to appear anywhere in argv for more flexible argument parsing. This is now a valid command, for example:

xbps-query -Rx --fulldeptree foo

This also improves some error messages instead of just printing the usage() naïvely.