Diff for Doc/Dev/ReleaseCycle between 2 and 3

+ Horde Release Cycle

This is an explanation of the Horde release model and the project's release rules.

* We will stick to [http://semver.org/ semantic versioning], this means:
  * APIs* keep backward compatible within the same major versions. If we have to break backward compatibility, Horde 4 becomes Horde 5 etc.
  * Adding features or extending APIs will bump the minor version, Horde 4.0 becomes Horde 4.1 etc.
* New versions will be released every half a year. Whether these are going to be major or minor version releases (or even just bug fix releases) depends on whether the changes since the last release broke BC or not.
  * Intermediate releases can be be done for security fixes or bug fixes.
* We will have sychronized releases of all application and framework components. If it's going to be a minor version release, only the modules that actually had any changes will be released. For major versions, all modules will be relased.
* Breaking backward compatibility will be documented, so that custom applications can be updated easily. See ((Doc/Dev/ConversionH4)) forand ((Doc/Dev/ConversionH5))for an example.
* The most recent two major versions will be maintained with security fixes, i.e. for at least 12 months.

*APIs in this context mean PHP APIs of framework components, external PHP APIs of applications, and external Horde RPC APIs.

See also ((Doc/Dev/Branches)) for an explanation of the branches used to prepare releases.