Clean up identity service RST

* Title casing
* s/identity server/identity service
* Rough column limit enforcement
* Add some links (used by future commits)

specification/identity_service_api.rst

@@ -1,6 +1,7 @@
 .. Copyright 2016 OpenMarket Ltd
 .. Copyright 2017 Kamax.io
 .. Copyright 2017 New Vector Ltd
+.. Copyright 2018 New Vector Ltd
 ..
 .. Licensed under the Apache License, Version 2.0 (the "License");
 .. you may not use this file except in compliance with the License.
@@ -56,7 +57,7 @@ is left as an exercise for the client.
 
 3PID types are described in `3PID Types`_ Appendix.
 
-API Standards
+API standards
 -------------
 
 The mandatory baseline for identity service communication in Matrix is exchanging
@@ -146,25 +147,24 @@ Key management
 
 An identity service has some long-term public-private keypairs. These are named
 in a scheme ``algorithm:identifier``, e.g. ``ed25519:0``. When signing an
-association, the Matrix standard JSON signing format is used, as specified in
+association, the standard `Signing JSON`_ algorithm applies.
-the server-server API specification under the heading "Signing Events".
 
 In the event of key compromise, the identity service may revoke any of its keys.
 An HTTP API is offered to get public keys, and check whether a particular key is
 valid.
 
-The identity server may also keep track of some short-term public-private
+The identity service may also keep track of some short-term public-private
 keypairs, which may have different usage and lifetime characteristics than the
 service's long-term keys.
 
 {{pubkey_is_http_api}}
 
-Association Lookup
+Association lookup
 ------------------
 
 {{lookup_is_http_api}}
 
-Establishing Associations
+Establishing associations
 -------------------------
 
 The flow for creating an association is session-based.
@@ -198,7 +198,7 @@ General
 
 {{associations_is_http_api}}
 
-Invitation Storage
+Invitation storage
 ------------------
 
 An identity service can store pending invitations to a user's 3pid, which will
@@ -241,10 +241,14 @@ Where the signature is produced using a long-term private key.
 Ephemeral invitation signing
 ----------------------------
 
-To aid clients who may not be able to perform crypto themselves, the identity service offers some crypto functionality to help in accepting invitations.
+To aid clients who may not be able to perform crypto themselves, the identity
-This is less secure than the client doing it itself, but may be useful where this isn't possible.
+service offers some crypto functionality to help in accepting invitations.
+This is less secure than the client doing it itself, but may be useful where
+this isn't possible.
 
 {{invitation_signing_is_http_api}}
 
 .. _`Unpadded Base64`:  ../appendices.html#unpadded-base64
 .. _`3PID Types`:  ../appendices.html#pid-types
+.. _`Signing JSON`: ../appendices.html#signing-json
+.. _`/3pid/onbind`: ../server_server.html#put-matrix-federation-v1-3pid-onbind