Update readme header

* Drop the Travis build status.
* Drop the link to projects since we're not using that GitHub feature
  anymore.
* Update the Binaries/Downloads link to point to tox.chat/downloads. The
  previous link just lead to a page telling the user to go to
  tox.chat/downloads.
* Update the code coverage badge to point to codecov.

README.md

@@ -1,9 +1,8 @@
 # ![Project Tox](https://raw.github.com/TokTok/c-toxcore/master/other/tox.png "Project Tox")
 
-**Current build status:** [![Build Status](https://travis-ci.org/TokTok/c-toxcore.svg?branch=master)](https://travis-ci.org/TokTok/c-toxcore)
-**Current Coverage:** [![Coverage Status](https://coveralls.io/repos/github/TokTok/c-toxcore/badge.svg?branch=master)](https://coveralls.io/github/TokTok/c-toxcore?branch=master)
+**Current Coverage:** [![coverage](https://codecov.io/gh/TokTok/c-toxcore/branch/master/graph/badge.svg?token=BRfCKo02De)](https://codecov.io/gh/TokTok/c-toxcore)
 
-[**Website**](https://tox.chat) **|** [**Wiki**](https://wiki.tox.chat/) **|** [**Blog**](https://blog.tox.chat/) **|** [**FAQ**](https://wiki.tox.chat/doku.php?id=users:faq) **|** [**Binaries/Downloads**](https://wiki.tox.chat/Binaries) **|** [**Clients**](https://wiki.tox.chat/doku.php?id=clients) **|** [**Compiling**](/INSTALL.md) **|** [**Toxcore's Projects**](https://github.com/TokTok/c-toxcore/projects)
+[**Website**](https://tox.chat) **|** [**Wiki**](https://wiki.tox.chat/) **|** [**Blog**](https://blog.tox.chat/) **|** [**FAQ**](https://wiki.tox.chat/doku.php?id=users:faq) **|** [**Binaries/Downloads**](https://tox.chat/download.html) **|** [**Clients**](https://wiki.tox.chat/doku.php?id=clients) **|** [**Compiling**](/INSTALL.md)
 
 **IRC Channels:** Users: [#[email protected]](https://web.libera.chat/#tox), Developers: [#[email protected]](https://web.libera.chat/#toktok)