Release 0.13.0 now available!

[Dean Michael Berris]

Hi Everyone!

I hope everyone had a great 2018! It's my pleasure to provide the
community with an updated "stable" release and I'd like to thank
everyone for the contributions to the 0.13-release branch!

As usual, you can get the latest from the website:

https://cpp-netlib.org

Thanks to everyone who's contributed to the 0.13-release branch! I
came up with this list with the following command:

`git checkout master && git log cpp-netlib-0.13.0-final.. --no-merges
--format=format:'%an (%ae)' | sort -u`

Andrey Khokhlov (bura...@gmail.com)
anonimal (anon...@i2pmail.org)
chenzhaoyu (chenz...@navercorp.com)
Daniel Nachbaur (daniel....@epfl.ch)
David Mugnai (d...@gnx.it)
David VandeBunte (davidva...@gmail.com)
Edward Kigwana (ekig...@users.noreply.github.com)
enrico.detoma (enrico...@gmail.com)
Frode (Frode)
Glyn Matthews (glyn.m...@gmail.com)
Gregor Jasny (gja...@googlemail.com)
Grzegorz Baran (grzegor...@sabre.com)
Håkon Løvdal (hlo...@gmail.com)
Hugo Maingonnat (hu...@deepomatic.com)
Igor Peshansky (igorpe...@github.com)
Igor Peshansky (ig...@google.com)
mtrenkmann (martin.t...@posteo.de)
Nabagata (ngsa...@gmail.com)
oneiric (33737923...@users.noreply.github.com)
Randy Du (ran...@gmail.com)
RyuaNerin (ad...@ryuanerin.kr)
Stefan Eilemann (eile...@gmail.com)
Uche Mennel (ume...@gmx.ch)
umennel (ume...@gmx.ch)
Yuval Hager (yha...@users.noreply.github.com)

Please enjoy the new release!

Cheers