fix: improve nuxt-content attrs handling

[benjamincanac]

Improve attrs handling on nuxt-content component so that you can pass class and id. Ensure to proxy these attributes to nuxt-content in dev mode with live editing.

Resolves #222, resolves #219.

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

nuxt-content component should be able to handle these use cases:

<nuxt-content :document="document" id="id-1" />
<nuxt-content :document="document" :id="`id-1`" />

<nuxt-content :document="document" class="class-1" />

<nuxt-content :document="document" :class="{ 'class-1': true }" />
<nuxt-content :document="document" :class="`class-1`" />
<nuxt-content :document="document" :class="['class-1']" />

<nuxt-content :document="document" class="class-1" :class="{ 'class-1': true }" />

[codecov-commenter]

Codecov Report

Merging #223 into dev will increase coverage by 0.83%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev     #223      +/-   ##
==========================================
+ Coverage   89.56%   90.39%   +0.83%     
==========================================
  Files          15       15              
  Lines         527      552      +25     
  Branches      107      118      +11     
==========================================
+ Hits          472      499      +27     
+ Misses         48       47       -1     
+ Partials        7        6       -1     

Impacted Files	Coverage Δ
lib/middleware.js	82.43% <0.00%> (-2.08%)	⬇️
lib/query-builder.js	96.90% <0.00%> (-1.91%)	⬇️
lib/utils.js	100.00% <0.00%> (ø)
lib/database.js	84.07% <0.00%> (+1.21%)	⬆️
lib/index.js	78.40% <0.00%> (+1.93%)	⬆️
lib/parsers/markdown/index.js	100.00% <0.00%> (+12.19%)	⬆️

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