Add and prefer Terminal.move_xy() over built-in 'move'

[jquast]

Closes #65.

[codecov]

Codecov Report

Merging #130 into master will increase coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #130      +/-   ##
==========================================
+ Coverage   79.89%   79.97%   +0.08%     
==========================================
  Files           8        8              
  Lines         925      929       +4     
  Branches      148      148              
==========================================
+ Hits          739      743       +4     
  Misses        171      171              
  Partials       15       15

Impacted Files	Coverage Δ
blessed/terminal.py	87.5% <100%> (+0.13%)	⬆️

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