Added "singleFile" crawler template.
Added packableFetchTree to Fetch.Tree
Added BinaryData constructor to Fetch.Types.Successor.FetchResult.
Renamed Crawlers.Linear.Load to Crawlers.Library and expanded it.

Crawlers.Library contains the static as well as the dynamically loaded
crawlers.
Removed guff from main file and CLI.

Other changes:
* renamed AppState.treeScripts to AppState.crawlers
* got rid of AppState's type argument.
* used the PackedCrawler type synonym in AppState.crawlers