WIP on append
use non-deprecated form of exception casting
offset storage happens right before writing compressed
add WIP for experimental source and sink objects
simplify the sink code a little
fix verbose printing
more append WIP
base class for compressed sinks
refactor into CompressedFPSource
PlainFPSink
update the documentation a little
fix spurious comma
fix invalid syntax
Merge branch 'feature/experimental_source_and_sink' into feature/append

merge for good measure, before it becomes too hard to merge

* feature/experimental_source_and_sink:
  update the documentation a little
  PlainFPSink
  refactor into CompressedFPSource
  base class for compressed sinks
  fix verbose printing
  simplify the sink code a little
  add WIP for experimental source and sink objects

Conflicts:
	bloscpack.py
factor out packaing a chunk to a fp
return the header too
add blosc_args as a parameter for append_fp
more WIP on append
basic syntax fixes
append_fp docstring