Initial commit of interface declaration
Stub ReleaseAddress method on all providers
Change error type
Change error type for local and manual providers
Implementation of ReleaseAddress for dummy provider
Test
Remove outdated comments
Merge pull request #1180 from voidspace/environ-releaseaddress

Add Environ.ReleaseAddress with dummy implementation

Environ.ReleaseAddress releases an ip address previously allocated using Environ.AllocateAddress. This adds it to the interface along with a simple dummy implementation.

(Review request: http://reviews.vapour.ws/r/491/)