Make timing tests less sensitive to slow test execution*

* See https://travis-ci.org/xolox/python-humanfriendly/jobs/28706938 but
  the same thing can happen anywhere. When looked at from that perspective
  the fix I'm committing here really isn't a fix, but I suspect it will be
  fine :-)

Restore Python 3.x compatibility (raw_input() -> input())

See https://travis-ci.org/xolox/python-humanfriendly/jobs/28700750

Unit tests for prompt_for_choice() (bringing coverage back up to 95%)

Merge pull request xolox#2: Added support for 'B' bytes unit to parse…

…_size

Improve prompt_for_choice(): Clearly present default choice (if any)

New prompt_for_choice() function

Enable spinner to show progress counter (percentage)

Make Timer() resumable

Make the Spinner(label=...) argument optional

Enable overriding of label for individual steps of spinner