Denote master version as 4.0.0 alpha

Also be more correct when reading the "xml:lang" attribute and remove superfluous whitespaces.

Fixes OF-977

Remove support for Legacy date/time (XEP-0090 and XEP-0091).

Delete web.xml.startup.servlet

Update admin.tld to use the latest taglib version.

Delete unused classes

OF-976 Language is not properly set in HttpSession

Language info should be in the Session, not in the Connection

Remove methods, which are both deprecated and unused.

Fix NPE when handling routing failures

Simplify and shorten pubsub message id

Update REST API plugin to 1.2.1

Avoids NPE by dropping (and optionally logging) error response stanzas
if the original packet has no sender JID.

The specification (XEP-0060) recommends generating unique message ids
within a pubsub instance to aid troubleshooting for notification
delivery issues when needed. This replaces a ridiculously long and
inefficient string concatenation with something a bit more tidy and
concise.

Fixed an cluster issue by create a chat room

These specifications are deprecated long enough (since 2007) in favor of XEP-202/203.

Extended the github readme

OF-115 Process S2S stanzas from a session serially

I feel the language (the stream's "xml:lang" attribute) should be in the Session interface rather than the Connection (similar as the stream id), because it's unrelated to the session's transport.

The HttpSession already did that.

Otherwise the used language is not easy to retrieve, e.g. when using SessionManager to get the session and OF-208 is hard to solve.

Alternatively we can expose the Connection in the Session interface, but this approach feels wrong to me.

Also use `java.util.Locale` rather than String, because it better reflects what can be in `xml:lang` (it can also have country codes, e.g. "de-CH")

Update web.xml schema namespaces to version 3.1 (Java EE 7)

Simplify/improve NIOConnection.deliver() by removing ByteBufferWriter.

For every packet being delivered the `ByteBufferWriter` creates a new String for every few chars written and puts it to the buffer.

According to my tests it is more efficient to create only one string and put it into the buffer once.
(10-20% better performance)

Old version 2.4 was J2EE 1.4

Also remove <taglib> from web.xml. This was required in JSP 1.2, but is no longer in JSP 2.0 (Servlet API 2.4) and gives warnings since it has been removed from the XSD.
See http://wiki.metawerx.net/wiki/RemovingTaglibFromWeb.xml

This is related to the JSP upgrade.

Some tags have changed after moving from the DTD to the XSD.
See also https://blogs.oracle.com/jluehe/entry/validate_your_tag_library_descriptor

Most likely not needed. It references a non-existent class.

This patch removes the thread pool from the ServerSocketReader, causing
stanzas from a particular S2S session to be processed serially on the same
thread used by the ServerSocketReader.

Each ServerSocketReader currently has a thread to itself, so this is unlikely
to have a serious impact on performance, but does have a very positive impact
on correctness.

https://community.igniterealtime.org/message/253510