* Add lb_t::sendpipe() that returns the pipe that was used for sending,
  similar to fq_t::recvpipe().
* Add forwarder functions to dealer_t to access these two.
* Add logic to req_t to ignore replies on pipes that are not the one
  where the request was sent.
* Enable test in test_spec_req.

Converted README to markdown

update Makefile to include new files

Problem: new spec test cases don't all work

* disabled the specific tests that do not work (yet) on libzmq
* cleaned up one source (test_spec_rep.c) but the others need similar work
* added sleep in test_spec_rep to allow connects time to happen; this would
  not be needed if we connected out to the REP peers instead in from them,
  but I didn't want to change the logic of the test code.

Make pipeline/reqrep tests try tcp:// endpoints.

The inproc:// endpoints sometimes use different code paths so
testing with regular tcp:// endpoints as well can show different
issues.

Add tests for Request-Reply and Pipeline pattern sockets.

[LIBZMQ-544] Fix compilation errors with Clang

Fix two unsigned comparisons to zero or more being always true. Clang
won't compile this with -Werror.

* See http://rfc.zeromq.org/spec:28/REQREP
* Not all testable statements are covered.
* At this point, there are several failures:
  - test_spec_req: The REQ socket does not correctly discard messages
    from peers that are not currently being talked to.
  - test_spec_dealer/router: On disconnect, the queues seem to not be
    emptied. The DEALER can still receive a message the disconnected
    peer sent, the ROUTER can still send to the identity of the dis-
    connected peer.

Fix tab/space formatting issue

Add monitor event for when monitoring is stopped so we can unblock any sockets waiting on monitor socket.

Fix cmake build

Fix build on windows, uint isn't a standard type, unsigned int is.

[LIBZMQ-541] pub socket sending fail issue

Implement socket type checking

Set socket buffers before establishing TCP connection 

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.

Problem: working with binary keys is painful

Minor code refactoring

Use generic session class whenever possible

The use of binary for CURVE keys is painful; you cannot easily copy
these in e.g. email, or use them directly in source code. There are
various encoding possibilities. Base16 and Base64 are not optimal.
Ascii85 is not safe for source (it generates quotes and escapes).

So, I've designed a new Base85 encoding, Z85, which is safe to use
in code and elsewhere, and I've modified libzmq to use this where
it also uses binary keys (in get/setsockopt).

Very simply, if you use a 32-byte value, it's Base256 (binary),
and if you use a 40-byte value, it's Base85 (Z85).

I've put the Z85 codec into z85_codec.hpp, it's not elegant C++
but it is minimal and it works. Feel free to rewrap as a real class
if this annoys you.

Problem: mechanisms are lagging behind specs

RFC23, RFC24, RFC26 now use variable-length command names that
end in null octet (valid C strings) instead of fixed-length
space padded strings.

Another ZMQ_STREAM simplification