doc,core: Read{Write,Only}Paths= and InaccessiblePaths=

This patch renames Read{Write,Only}Directories= and InaccessibleDirectories=
to Read{Write,Only}Paths= and InaccessiblePaths=, previous names are kept
as aliases but they are not advertised in the documentation.

Renamed variables:
`read_write_dirs` --> `read_write_paths`
`read_only_dirs` --> `read_only_paths`
`inaccessible_dirs` --> `inaccessible_paths`

shell-completion/bash/systemd-run

@@ -84,8 +84,8 @@ _systemd_run() {
                          LimitNICE= LimitRTPRIO= LimitRTTIME= PrivateTmp= PrivateDevices=
                          PrivateNetwork= NoNewPrivileges= WorkingDirectory= RootDirectory=
                          TTYPath= SyslogIdentifier= SyslogLevelPrefix= SyslogLevel=
-                         SyslogFacility= TimerSlackNSec= OOMScoreAdjust= ReadWriteDirectories=
-                         ReadOnlyDirectories= InaccessibleDirectories= EnvironmentFile=
+                         SyslogFacility= TimerSlackNSec= OOMScoreAdjust= ReadWritePaths=
+                         ReadOnlyPaths= InaccessiblePaths= EnvironmentFile=
                          ProtectSystem= ProtectHome= RuntimeDirectory= PassEnvironment='
 
             COMPREPLY=( $(compgen -W '$comps' -- "$cur") )