Some doc fixes (#315)

#docs_client.rst:
- 257: Add proper eplanation of callback, like in every other method
- 433: Fix linking for Invite Resolvable

#docs_message.rst:
- 90 : Replace ':' with '-', just for consistency with the others

#docs_resolvables.rst:
- 92 : String doesn't link to anything (?) -> Link removed

#docs_servers.rst:
- 109 : Properly indent code-block because it didn't show at all on rtfd

#docs_serverchannel.rst:
- 53 : Remove doulbe '`' causing it not to display properly

#docs_voiceconnection.rst:
- 67 : Remove 'currently, it currently

#docs_voiceconnection.rst:
- 32 : Add links for Role Resolvable, as used in client#addMemberToRole,
client#removeMemberFromRole and client#memberHasRole

docs/docs_server.rst

@@ -106,12 +106,12 @@ Returns an object containing metadata of a user within the server, containing a
 .. code-block:: js
 
 	{
-		joinedAt : 1449339323747,
-        roles: [],
-        mute : false,
-        self_mute : false,
-		deaf : false,
-        self_deaf : false
+		joinedAt: 1449339323747,
+		roles: [],
+		mute: false,
+		self_mute: false,
+		deaf: false,
+		self_deaf: false
 	}
 
 leave()