Correctly decode non-ASCII tEXt chunks and support encoding them

[targos]

Refs: #26

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (395ecee) 91.54% compared to head (c645b96) 92.20%.

❗ Current head c645b96 differs from pull request most recent head 58b383c. Consider uploading reports for the commit 58b383c to get more accurate results

Files	Patch %	Lines
src/helpers/crc.ts	96.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
+ Coverage   91.54%   92.20%   +0.65%     
==========================================
  Files           9       10       +1     
  Lines         426      462      +36     
  Branches       84       87       +3     
==========================================
+ Hits          390      426      +36     
  Misses         36       36              

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[targos]

I'm working on the encoder.

[targos]

Done. I removed keyword-specific character validation because the spec says that decoders should be lenient: https://www.w3.org/TR/png/#13Text-chunk-processing

[lpatiny]

LGTM