Outsource key input to Blessed

[thomasballinger]

Rip out the innards of a curtsies.input.Input object and replace with calls to Blessed.Terminal.inkey()

[thomasballinger]

Potential issues so far:

• can't set which stdin to use for cbreak (this is probably fine)
• find out if Blessed does the VDSUSP trick on Macs/BSD (find issue for this, it's been talked about before)
• find out behavior of inkey if SIGTSTP via dsusp happens (preventable, just turn of dsusp)
• How to block on stdin and other file descriptors simultaneously (we still have access to sys.stdin)
• blocked on resolution of Support comparators for matching keyboard input to meta and ctrl keys jquast/blessed#58 which I assume will start grouping escape-prepended keys instead of reporting them separately

Plan: move paste detection into bpython, based on nonblocking readaheads instead of number of raw bytes read