* fixed VZ decompressoin and add some checks
* add get_manifest() which returns a list of CDNDepotManifest for app_id and branch
* add iter_files() which will get all manifests, and iter files for app_id and branch
* add get_manifest_for_workshop_item() can be used to download steampiped hosted workshop items
* add basic caching inside CDNClient
* CDNDepotManifest, which enhances DepotManifest and inits CDNDepotFiles
* CDNDepotFile expands DepotFile to a file like object that can be used to directly seek and
read files from steampipe
* DepotFile for Manifest mappings
* CDNClient now handles content servers selection better
* CDNClient can auto get and cache cdn auth tokens and depot keys
* added get_chunk() to CDNClient, only ZIP compression, TODO LZMA
Rossen Georgiev