Updated test code to download a new consensus document each time.
Added print statements for debugging.
Added comment with potential solution to zlib error in the _get_remote_document() method.
Moved Zlib decompression logic from docdownloader.py's children to docdownloader.py
Updated code to redownload compressed documents if a decompression failure occurs.
Start refactoring cells to be immutable
Updated comments and log messages.
added cell field definitions
added utility 'pack_cell'; implemented auth_challenge
Began immutable `DestroyCell`.
Merge branch 'ImmutableCells' of https://github.com/nskinkel/309Project into ImmutableCells
Made `NetInfoCell` immutable.

Also made one last change to `DestroyCell`.
added immutable cells: AuthChallenge, Certs, Create2, Created2 and some utility functions
add immutable versions cell
Implemented immutable `RelayExtend2Cell`.
Merge branch 'ImmutableCells' of https://github.com/nskinkel/309Project into ImmutableCells

Conflicts:
	oppy/cell/util.py
Made some fixes to `RelayExtend2Cell`.
started migration of full codebase to using immutable cells
Merge branch 'NetstatusZLib' into ImmutableCells
finish immutable cell migration