Add a default style to themes which gets applied to "everything else".

[mkantor]

The new default key in themes allows configuring the "base" style for substrings not handled by highlight.js. The specifics depend on the language but this typically includes things like commas in parameter lists, semicolons at the end of lines, etc.

For example, here's how the JSON fixture looks in my console with no styles set:

And here it is with default set to dim:

[codecov]

Codecov Report

Merging #61 into master will increase coverage by 1.38%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #61      +/-   ##
==========================================
+ Coverage   65.95%   67.34%   +1.38%     
==========================================
  Files           2        2              
  Lines          47       49       +2     
  Branches        5        6       +1     
==========================================
+ Hits           31       33       +2     
  Misses         16       16

Impacted Files	Coverage Δ
src/theme.ts	36.36% <ø> (ø)	⬆️
src/index.ts	92.59% <100%> (+0.59%)	⬆️

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[mkantor]

@felixfbecker have you had a chance to look at this yet?

[felixfbecker]

🎉 This PR is included in version 2.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀