Refactoring page link that will be put in the queue
Add SubsiteID to a links if Subsite extensions exists on those pages
If urls contain SubsiteID generate domain specific caches
In subsite mode, generate the main site into cache subdirectory too.
RebuildStaticCache task can queue pages with subsite extension
Remove legacy code, no longer needed.
BUG Nest configuration to prevent global state spillover.
Remove staticpublisher dependency by copying FilesystemPublisher.
NEW Smuggle object's metadata in the URL that gets enqueued.

Context information is necessary in some situations such as selecting
a subsite, or detecting ErrorPages. The object tied to the URL is now
smuggled in the URL using _ID and _ClassName get parameters.
NEW Interfaces: StaticallyPublishable and StaticPublishingTrigger

Define two major behaviours related to static publisher: triggering
updates in objects, and defining URLs that an object wishes to
statically publish.
NEW Provide standard publishable and trigger implementation for SiteTree
Theme was not correctly set on subsites

This was because the config system tried to use non existing class StaticPublisher, moved it do use FilesystemPublisher instead
Fixing unit tests to report failures instead of error
BUG Remove debug statements.
NEW Add PublishableRedirectorPage.
BUG Merge redirectors in properly. Add test.
Update documentation for the new interfaces and configuration.
Rename the RebuildStaticCacheTask to SiteTreeFullBuildEngine.
BUG Fix cache file deletions for subsites and during publishing.

Split the delete function (unpublishPagesAndStaleCopies) into two
functions that separately handle deletions of regular and stale files.
Also provide a helper convertUrlsToPathMap which encapsulates some of
the complexity of making subsites publish into directiories.

The following two features are being fixed here:
- Make the deletions aware of subsites - files need to be deleted
from subdirectories if we are running in the subsites mode.
- Regular cache files need to be deleted on page modifications,
while the stale pages stay behind until the builder queue is executed.
This was originally working, but was broken with 2.0 refactor.
Remove the functional test which no longer applies. Setup travis.

The test being removed assumed that the module's user will not customise
the behaviour of the SiteTree publishing. The test would work with the
default publishable decorators, but as soon as someone implemented their
own the test would start breaking.

This is better covered by the decorator-specific PublishableSiteTreeTest