Rename doc/mapformat.txt and update doc to match SRP changes

The documentation file contains not just information about the
map itself, but also about further files inside the world's
directory.

Documentation didn't reflect recent SRP addition, now it does.

doc/worldformat.txt

@@ -41,13 +41,21 @@ auth.txt
 ---------
 Contains authentication data, player per line.
   <name>:<password hash>:<privilege1,...>
-Format of password hash is <name><password> SHA1'd, in the base64 encoding.
+
+Legacy format (until 0.4.12) of password hash is <name><password> SHA1'd,
+in the base64 encoding.
+
+Format (since 0.4.13) of password hash is #1#<salt>#<verifier>, with the parts inside <> encoded in the base64 encoding.
+<verifier> is an RFC 5054 compatible SRP-2048-SHA1 verifier
+of the given salt, password, and the player's name lowercased.
 
 Example lines:
 - Player "celeron55", no password, privileges "interact" and "shout":
     celeron55::interact,shout
-- Player "Foo", password "bar", privilege "shout":
+- Player "Foo", password "bar", privilege "shout", with a legacy password hash:
     foo:iEPX+SQWIR3p67lj/0zigSWTKHg:shout
+- Player "Foo", password "bar", privilege "shout", with an up to date pw hash (yes it is THAT long):
+    foo:#1#hPpy4O3IAn1hsNK00A6wNw#Kpu6rj7McsrPCt4euTb5RA5ltF7wdcWGoYMcRngwDi11cZhPuuR9i5Bo7o6A877TgcEwoc//HNrj9EjR/CGjdyTFmNhiermZOADvd8eu32FYK1kf7RMC0rXWxCenYuOQCG4WF9mMGiyTPxC63VAjAMuc1nCZzmy6D9zt0SIKxOmteI75pAEAIee2hx4OkSXRIiU4Zrxo1Xf7QFxkMY4x77vgaPcvfmuzom0y/fU1EdSnZeopGPvzMpFx80ODFx1P34R52nmVl0W8h4GNo0k8ZiWtRCdrJxs8xIg7z5P1h3Th/BJ0lwexpdK8sQZWng8xaO5ElthNuhO8UQx1l6FgEA:shout
 - Player "bar", no password, no privileges:
     bar::