[WIP] Upgrade to prompt_toolkit 2.0

[jonathanslenders]

Upgrade to prompt_toolkit 2.0.
As far as I could test, it looks like most stuff is working fine.
I still have to check the ignore_case option.

[jonathanslenders]

See also: prompt-toolkit/python-prompt-toolkit#568

[j-bennet]

@jonathanslenders Thank you! I think rebasing on top of master should fix the things breaking in travis.

[jonathanslenders]

I just rebased.
What things did you see breaking? Prompt_toolkit still supports Python 2.6, but version 2.0 is not released yet, so I'm not sure the tests will pass.

[j-bennet]

@jonathanslenders I removed 2.6 and 3.3 from travis, because py.test refuses to install with those versions anymore. But the build breaks with this now:

  Could not find a version that satisfies the requirement prompt_toolkit<2.1.0,>=2.0.0 (from wharfee==0.10) (from versions: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 0.9, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.25, 0.26, 0.28, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 1.0.0, 1.0.1, 1.0.2, 1.0.3, 1.0.4, 1.0.5, 1.0.6, 1.0.7, 1.0.8, 1.0.9, 1.0.10, 1.0.13, 1.0.14, 1.0.15)
No matching distribution found for prompt_toolkit<2.1.0,>=2.0.0 (from wharfee==0.10)
Command exited with code 1

So yes, it needs a 2.0 release.