add support for bracketed paste

[joshuarubin]

Attempting to resolve #120
Does not support windows yet, but shouldn't be too hard to define a separate paste.go file for windows with the correct event information.

Rebased since #137

It's been so long that I'm not sure how to test it, but it looks right to me.

[codecov]

Codecov Report

Merging #286 into master will decrease coverage by 0.24%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #286      +/-   ##
==========================================
- Coverage   19.58%   19.34%   -0.25%     
==========================================
  Files          17       18       +1     
  Lines        1445     1463      +18     
==========================================
  Hits          283      283              
- Misses       1146     1164      +18     
  Partials       16       16

Impacted Files	Coverage Δ
key.go	0% <ø> (ø)	⬆️
tscreen.go	0% <0%> (ø)	⬆️
paste.go	0% <0%> (ø)

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[gdamore]

This will need to be refactored in terms of the terminal descriptions. I'm not at all convinced that bracketed paste keys are universal, and I worry about possible collisions elsewhere.

[gdamore]

I've taken a different approach to this, and am also requiring applications to opt in. See #395 for my solution.