Add failing test for curses hline and vline support

[wileykestner]

This pull request is meant to be the starting point for a discussion and is not intended as a candidate for acceptance as-is.

I'd love to write integration tests for curses applications using hecate. To get started, I wrote a trivial curses application, box.py. When box.py is run, the screen should have this box in the upper left hand corner (and typing q should cause box.py to exit):

┌──────────┐
│I am a box│
└──────────┘

I wrote a hecate test that asserts what the screen should look when box.py runs.

The current out-of-the-box configuration results in a captured screen that looks like this when run through the Runner class:

lqqqqqqqqqqk
xI am a boxx
mqqqqqqqqqqj

I'd be quite interested in digging in and creating another commit as part of this pull request that implements the feature, but because I'm so unfamiliar with the core problem domain, I thought I would first propose the feature request in the form of a failing test and ask for the author's guidance, if any.

[thijstriemstra]

ping @DRMacIver