Added docs as asciidoctor with cross platform support. (#5733)

* Added docs as asciidoctor with cross platform support.

* Fixed release script with new doc building mechanism.

doc/api/changeset_library.adoc

@@ -0,0 +1,46 @@
+== Changeset Library
+
+The https://github.com/ether/etherpad-lite/blob/develop/src/static/js/Changeset.js[changeset
+library]
+provides tools to create, read, and apply changesets.
+
+=== Changeset
+
+[source,javascript]
+----
+const Changeset = require('ep_etherpad-lite/static/js/Changeset');
+----
+
+A changeset describes the difference between two revisions of a document. When a
+user edits a pad, the browser generates and sends a changeset to the server,
+which relays it to the other users and saves a copy (so that every past revision
+is accessible).
+
+A transmitted changeset looks like this:
+
+[source]
+----
+'Z:z>1|2=m=b*0|1+1$\n'
+----
+
+=== Attribute Pool
+
+[source,javascript]
+----
+const AttributePool = require('ep_etherpad-lite/static/js/AttributePool');
+----
+
+Changesets do not include any attribute key–value pairs. Instead, they use
+numeric identifiers that reference attributes kept in an https://github.com/ether/etherpad-lite/blob/develop/src/static/js/AttributePool.js[attribute pool].
+This attribute interning reduces the transmission overhead of attributes that
+are used many times.
+
+There is one attribute pool per pad, and it includes every current and
+historical attribute used in the pad.
+
+=== Further Reading
+
+Detailed information about the changesets & Easysync protocol:
+
+* https://github.com/ether/etherpad-lite/blob/develop/doc/easysync/easysync-notes.pdf[Easysync Protocol]
+* https://github.com/ether/etherpad-lite/blob/develop/doc/easysync/easysync-full-description.pdf[Etherpad and EasySync Technical Manual]