v0.1.0

v0.1.0 is a moderate API change through an almost-total-refactor of the Accessor code. It introduces:

• A simpler API. No more Accessor, Query, and GroupbyApplier—just Accessor.
• This allows operation chaining all the time, not just when grouping.
• A progress bar. Finally.
• A completed README
• The PREREQUISITES document
• Explicit requirement of pandas v0.18.1 (see #10)

At least 0.1 is better than 0.0, eh?