Enhancement: Smaller Interpreter Suggestion Footprint

[tigh-latte]

Currently, if you import the interpreter and type interpreter. a lot of options that aren't related to using the interpreter appear, this could overwhelming and create the impression that the package is harder to use than it actually is.

To address this I've:

• moved errors into their own subpackage
• moved the scriptflags into their own subpackage.
• Removed the NewOpcodeParser function and instead provided a DefaultOpcodeParser struct which implements the OpcodeParser interface is useful from zero value.

And with this, package usage is friendlier upon import:

[codecov-commenter]

Codecov Report

Merging #51 (079e1e8) into master (25661c5) will decrease coverage by 0.02%.
The diff coverage is 88.37%.

❗ Current head 079e1e8 differs from pull request most recent head 08684a8. Consider uploading reports for the commit 08684a8 to get more accurate results

@@            Coverage Diff             @@
##           master      #51      +/-   ##
==========================================
- Coverage   85.98%   85.96%   -0.03%     
==========================================
  Files          26       26              
  Lines        2862     2871       +9     
==========================================
+ Hits         2461     2468       +7     
- Misses        272      275       +3     
+ Partials      129      128       -1     

Impacted Files	Coverage Δ
bscript/interpreter/errs/error.go	50.00% <0.00%> (ø)
bscript/interpreter/opcodeparser.go	80.55% <72.09%> (+3.25%)	⬆️
bscript/interpreter/thread.go	90.74% <86.11%> (+0.17%)	⬆️
bscript/interpreter/operations.go	96.16% <97.64%> (+0.03%)	⬆️
bscript/interpreter/engine.go	100.00% <100.00%> (ø)
bscript/interpreter/scriptnum.go	100.00% <100.00%> (ø)
bscript/interpreter/stack.go	93.87% <100.00%> (-0.39%)	⬇️

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[theflyingcodr]

Good call, LGTM