* Removed the `Directory` argument to `didSearchPaths`.
Now each searcher gets its own instance of `didSearchPaths` that is parameterized by provider.
* Simplified `DefaultDirectorySearcher.search()` so it creates one `DirectorySearch`
rather than one per `Directory` passed to `search()`.
* `search()` takes an array of `Directory` objects rather than an individual object.
* `options.didSearchPaths` now takes the `Directory` in addition to the `count` as an argument.
1. Update documentation for `default-directory-search.coffee`.
2. Ensure that multiple `DirectorySearch` searches are run in series rather than in parallel to conserve resources.
The contract for a provider for the `atom.directory-searcher` service
is defined by the spec of the `DefaultDirectorySearcher`.
This modifies `Workspace::scan()` to use the appropriate `DirectorySearcher`
for each member of `atom.project.getDirectories()` when scanning the workspace
for files that match the specified regex.
