Get rid of the dev branch

Its existence hasn't added anything in several years, and I keep
forgetting to merge it into master after releases.

CONTRIBUTING.md

@@ -7,9 +7,11 @@ A general guide to contributing to LOOT may be found on [LOOT's website](https:/
 
 The repository branching structure is pretty simple:
 
-* The `master` branch holds released code.
-* The `dev` branch is a next-release branch. It holds code that's working towards the next big release but which isn't there yet. Code on `dev` is generally pretty stable as CI must pass before anything can be merged into it, but may not be release-ready.
-* Other branches are generally themed on specific features or groups of changes, and come and go as they are merged into one of the two above, or discarded.
+* The `master` branch holds code that's released or that will be in the next
+  release. Code on `master` is generally pretty stable as CI must pass before
+  anything can be merged into it.
+* Other branches are generally themed on specific features or groups of changes,
+  and come and go as they are merged into one of the two above, or discarded.
 
 ## Getting Involved
 

README.md

@@ -1,7 +1,7 @@
 # libloot
 
-[![AppVeyor Build Status](https://ci.appveyor.com/api/projects/status/48a540m7ywuqcl3b/branch/dev?svg=true)](https://ci.appveyor.com/project/LOOT/libloot/branch/dev)
-[![Travis Build Status](https://travis-ci.org/loot/libloot.svg?branch=dev)](https://travis-ci.org/loot/libloot)
+[![AppVeyor Build Status](https://ci.appveyor.com/api/projects/status/48a540m7ywuqcl3b/branch/master?svg=true)](https://ci.appveyor.com/project/LOOT/libloot/branch/master)
+[![Travis Build Status](https://travis-ci.org/loot/libloot.svg?branch=master)](https://travis-ci.org/loot/libloot)
 [![Documentation Status](https://readthedocs.org/projects/loot-api/badge/?version=latest)](http://loot-api.readthedocs.io/en/latest/?badge=latest)
 
 ## Introduction