luahttp: bump API and document /art changes

(cherry picked from commit 488f94b14be6564b96eba3a59ad0d404fd287f8d)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

share/lua/http/requests/README.txt

@@ -22,6 +22,16 @@ where path attributes are provided in output, these should be ignored in favour
 path support is scheduled to be removed entirely from 1.3
 ---
 
+<root> (/)
+===========
+
+
+> Get album art for current input:
+  /art  (NB: not /requests/art)
+
+> Get album art for any playlist input (available from API version 3):
+  /art?item=123  (NB: not /requests/art)
+
 
 status.xml or status.json
 ===========

share/lua/intf/modules/httprequests.lua

@@ -432,7 +432,7 @@ local aout = vlc.object.aout()
     local s ={}
 
     --update api version when new data/commands added
-    s.apiversion=2
+    s.apiversion=3
     s.version=vlc.misc.version()
     s.volume=vlc.volume.get()