Add line length specifier to assembler

[craigthomas]

This PR adds a line length specifier as an option to the assembler as --print_length. This controls how many characters are allowed to be printed to the standard output when asking the assembler to --print the output of assembly. Integration test added to catch new conditions. This PR closes #84

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.93%. Comparing base (cf0e679) to head (05fd23e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #101      +/-   ##
==========================================
+ Coverage   94.92%   94.93%   +0.01%     
==========================================
  Files          16       16              
  Lines        2050     2055       +5     
==========================================
+ Hits         1946     1951       +5     
  Misses        104      104              

Files with missing lines	Coverage Δ
cocoasm/program.py	99.35% <100.00%> (-0.02%)	⬇️
cocoasm/statement.py	99.51% <100.00%> (+0.01%)	⬆️

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