Feature pithoschanges

Includes the necessary changes for better integration with Pithos

Noticeable changes:

* Add signature for v2 maps
* Add v0 map hint
* Support map creation from a given object list
* Remove "archip_" prefix from maps and blocks created by archipelago
* Add rename functionality
* Immediately delete writeable objects when removing a map
* Add readonly option when mapping a volume
Actually it doesn't matter who the caller is, Pithos or anybody else. If you want to access a v0 mapfile from archipelago, you must set the XF_CONTADDR flag in flags and optionally the contaddr_size. Setting the contaddr_size only, does not have any effect, and it is ignored by the mapper.