error: add docstrings

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

src/error.rs

@@ -21,12 +21,19 @@ use xmpp_parsers::{Error as ParserError, FullJid, Jid};
 
 #[derive(Debug)]
 pub enum Error {
+    /// Raised when editing an occupant with a non-matching session JID.
     MismatchJids(Jid, Jid),
+    /// Raised when a new occupant tries to use a nickname already assigned in the room.
     NickAlreadyAssigned(String),
+    /// Raised when editing or fetching an occupant with a session that isn't associated with the
+    /// occupant.
     NonexistantSession(FullJid),
     SessionAlreadyExists(FullJid),
+    /// Raised when fetching an occupant with a nickname that isn't assigned in the room.
     ParticipantNotFound(String),
+    /// TokioXMPP errors
     Xmpp(Box<TokioXMPPError>),
+    /// Parser errors
     Parser(Box<ParserError>),
 }