WIP: Replace tcell with termbox

[kimtore]

This is a refactoring commit that will replace the tcell library with the simpler termbox.

• Fixes Pasting more than 11 characters doesn't work #107
• Fixes Nil pointer dereference when starting PMS in certain terminals #66

[codecov-io]

Codecov Report

Merging #108 into master will decrease coverage by 0.35%.
The diff coverage is 54.02%.

@@            Coverage Diff             @@
##           master     #108      +/-   ##
==========================================
- Coverage   53.26%   52.91%   -0.36%     
==========================================
  Files          51       55       +4     
  Lines        1821     1905      +84     
==========================================
+ Hits          970     1008      +38     
- Misses        828      870      +42     
- Partials       23       27       +4

Impacted Files	Coverage Δ
options/defaults.go	0% <ø> (ø)	⬆️
commands/redraw.go	0% <0%> (ø)	⬆️
commands/list.go	0% <0%> (ø)	⬆️
term/canvas.go	0% <0%> (ø)
commands/cursor.go	64.35% <0%> (+1.85%)	⬆️
commands/viewport.go	45.34% <0%> (-0.54%)	⬇️
commands/style.go	83.33% <100%> (-1.39%)	⬇️
keysequence/keysequence.go	22.72% <20%> (-39.28%)	⬇️
term/sampler.go	64.28% <64.28%> (ø)
term/keypress.go	71.69% <71.69%> (ø)
... and 6 more

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