* Command names changed from null terminated to length-specified
* Command frames use the correct flag (bit 2)
* test_stream acts as test case for command frames
* Some code cleanups

The window scale option carried in SYN segment is computed from socket's
receive buffer size. So we need to set this buffer size before calling
connect or bind.

Also tidy up monitor test a little.

- we need to switch to PLAIN according to options.mechanism
- we need to catch case when both peers are as-server (or neither is)
- and to use username/password from options, for client

This implements protocol handshake.
We still need to design and implement 1) API changes so a user
can set username and password, and 2) a mechanism for engine
to authenticate users.

The patch makes the code somewhat simpler and prepares it for
more complex initialization handshakes.

* Starting draft ZMTP/2.1 protocol (revision 2)
* Basis for adding security to the wire protocol
* Maintains backward compatibility

Copyrights had become ads for Sustrik's corporate sponsors, going against the original
agreement to share copyrights with the community (that agreement was: one line stating
iMatix copyright + one reference to AUTHORS file). The proliferation of corporate ads
is also unfair to the many individual authors. I've removed ALL corporate title from
the source files so the copyright statements can now be centralized in AUTHORS and
source files can be properly updated on an annual basis.

When we send a large message, the message can be splitted into two chunks.
One is in the encoder buffer and the other is the zero-copy pointer.
The session could get the term before the last chunk is sent.

Copy monitor specific event endpoints to event messages as the engine etc. can be released at anytime

This reverts commit 1a18c7b0, reversing
changes made to bef9a41b.

Ref: https://zeromq.jira.com/browse/LIBZMQ-459

    - Created a new option ZMQ_ROUTER_RAW_SOCK
    - Added new raw_encoder and raw_decoder to receive and send messages in raw form to remote client
    - Added test case file tests/test_raw_sock.cpp

    o To create a raw router sock set the ZMQ_ROUTER_RAW_SOCK option
    o ZMQ_MSGMORE flag is ignored for non-id messages
    o To terminate a remote connection send id message followed by zero length data message

See also https://zeromq.jira.com/browse/LIBZMQ-433

Significantly reworked the monitoring infrastructure with a more granular per socket API and to play well with monitoring endpoints in application threads

This is supposed to become part of the ZMTP/1.1.

The main differences from the ZMTP/1.0 framing protocol are:
- flags field comes first, followed by the length field
- long messages are signaled using a flag rather then 0xff escape
- length field does not include the flags field, 0 is a valid value

Since ZMQ 2.x does not support subscription forwarding, it's not
possible to use ZMQ 2.x SUB socket to receive messages from a PUB
socket.

This patch adds some compatibility layer so that ZMQ 2.x SUB socket
receives messages from PUB socket.

This patch introduces i_msg_sink and i_msg_source interfaces. This
allows us to make message encoder and decoder more general.