Fix links in README.md

Reference-style links catch everyone by surprise.
Merge pull request #1 from mpalmer/fix-readme-md

Fix links in README.md
Document lack of thread-safety in marquise_consumer
Build zmq4 rather than relying on packaged zmq3 in travis build
Allow setting of POLLER_EXPIRY
Poller expiry needs to be a ull
All text is treated as UTF-*
Implement first half of defer file cleanup/retry utility

It will currently delete any unused zero-length deferral file and try to
retrieve messages from unused nonzero-length deferral files, but apart
from reporting the number of messages retrieved it does not retry those
messages or otherwise modify those files.

Squashed commit of the following:

commit a9289e80756fd3ccb1104b6d462986599a9507c9
Author: Sharif Olorin <sio@tesser.org>
Date:   Thu Mar 20 10:04:24 2014 +1100

    Fix segfault on failure to stat

commit cfd759e053c8ebca58eaec6c5e9eb1dcbafd220d
Author: Sharif Olorin <sio@tesser.org>
Date:   Wed Mar 19 19:36:24 2014 +1100

    [wip] retry sends in deferral processor

commit 3fc52c018e1dd98a22831f7c0a675edc99a980d8
Author: Sharif Olorin <sio@tesser.org>
Date:   Wed Mar 19 17:50:05 2014 +1100

    Should actually shut down before dying

commit f20a62be9b3000377a4d78fd0074487fb4fa46b6
Author: Sharif Olorin <sio@tesser.org>
Date:   Wed Mar 19 17:47:49 2014 +1100

    Retrieve bursts from non-empty deferral files

commit eed00b769367f20ab52517bda6722c1c97fecad8
Author: Sharif Olorin <sio@tesser.org>
Date:   Wed Mar 19 17:24:00 2014 +1100

    Shutdown libmarquise poller

commit 32a725a25c1740b83f6fb566e2bcdab3644c0b7c
Author: Sharif Olorin <sio@tesser.org>
Date:   Wed Mar 19 17:06:02 2014 +1100

    Initialize poller thread

commit c7a6c66f94ce00f850b1afc9866a75d90c2836b9
Author: Sharif Olorin <sio@tesser.org>
Date:   Tue Mar 18 20:40:53 2014 +1100

    Clean up process_deferrals a bit

commit cfed20aeae5f8bfcc403231f4423fd5b352ec6b9
Author: Sharif Olorin <sio@tesser.org>
Date:   Tue Mar 18 20:25:29 2014 +1100

    [wip] utility to clean up/retry old deferral files
Merge branch 'wip-set-timeout'

 to explain why this merge is necessary,
Add telemetry setup to marquised
document implementation of LIBMARQUISE_TELEMETRY_DEST
Set marquised listen sock HWM to unlimited

As is, the socket may block on writes from libmarquise clients, which is
Bad.
remove superfluous ack read on client threa
Remove unused label
bugfix edge cases where 0mq buffers fill
release 1.2.0
Make README a symlink to README.md
Fix off-by-one in hwm reporting
Add link to packages repo in README