Redo how the repository keys are stored.

- Repository keys are now stored in a new directory on metadir (/var/db/xbps):

	<metadir>/key>

- Repository keys are stored with the hex fingerprint of its RSA
  public key in a plist dictionary:

	<metadir>/keys/xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx.plist

- Drop xbps-rkeys(8) and merge its functionality into xbps-install(8) and
  xbps-query(8).

- xbps-query(8) -vL now shows some more details of remote repositories:

 3134 http://localhost:8000 (RSA signed, verified)
      Signed-by: Void Linux
      4096 60:ae:0c:d6:f0:95:17:80:bc:93:46:7a:89:af:a3:2d
   16 http://localhost:8000/nonfree (RSA signed, verified)
      Signed-by: Void Linux
      4096 60:ae:0c:d6:f0:95:17:80:bc:93:46:7a:89:af:a3:2d

Bump XBPS_API_VERSION.