Merge pull request mopidy#1055 from jodal/docs/add-semver-section

docs: Add section on semantic versioning

docs/versioning.rst

@@ -2,22 +2,36 @@
 Versioning
 **********
 
-Mopidy uses `Semantic Versioning <http://semver.org/>`_, but since we're still
-pre-1.0 that doesn't mean much yet.
+Mopidy follows `Semantic Versioning <http://semver.org/>`_. In summary this
+means that our version numbers have three parts, MAJOR.MINOR.PATCH, which
+change according to the following rules:
+
+- When we *make incompatible API changes*, we increase the MAJOR number.
+
+- When we *add features* in a backwards-compatible manner, we increase the
+  MINOR number.
+
+- When we *fix bugs* in a backwards-compatible manner, we increase the PATCH
+  number.
+
+The promise is that if you make a Mopidy extension for Mopidy 1.0, it should
+work unchanged with any Mopidy 1.x release, but probably not with 2.0. When a
+new major version is released, you must review the incompatible changes and
+update your extension accordingly.
 
 
 Release schedule
 ================
 
 We intend to have about one feature release every month in periods of active
-development. The feature releases are numbered 0.x.0. The features added is a
-mix of what we feel is most important/requested of the missing features, and
-features we develop just because we find them fun to make, even though they may
-be useful for very few users or for a limited use case.
-
-Bugfix releases, numbered 0.x.y, will be released whenever we discover bugs
-that are too serious to wait for the next feature release. We will only release
-bugfix releases for the last feature release. E.g. when 0.14.0 is released, we
-will no longer provide bugfix releases for the 0.13 series. In other words,
-there will be just a single supported release at any point in time. This is to
-not spread our limited resources too thin.
+development. The features added is a mix of what we feel is most
+important/requested of the missing features, and features we develop just
+because we find them fun to make, even though they may be useful for very few
+users or for a limited use case.
+
+Bugfix releases will be released whenever we discover bugs that are too serious
+to wait for the next feature release. We will only release bugfix releases for
+the last feature release. E.g. when 1.2.0 is released, we will no longer
+provide bugfix releases for the 1.1.x series. In other words, there will be just
+a single supported release at any point in time. This is to not spread our
+limited resources too thin.