Add disallow_invalid_utf8 option for decoding

[sile]

This PR adds reject_invalid_utf8 option.
By setting the option with the value false when decoding, you can reject JSON strings that contain invalid UTF-8 byte sequences.
See also: #37

[codecov-io]

Codecov Report

Merging #44 into master will decrease coverage by 0.01%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #44      +/-   ##
==========================================
- Coverage   88.38%   88.37%   -0.02%     
==========================================
  Files           3        3              
  Lines         267      344      +77     
==========================================
+ Hits          236      304      +68     
- Misses         31       40       +9

Impacted Files	Coverage Δ
src/jsone.erl	38.46% <ø> (+9.89%)	⬆️
src/jsone_decode.erl	98.34% <66.66%> (-0.81%)	⬇️
src/jsone_encode.erl	88.83% <0%> (+3.64%)	⬆️

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