Preserve directive content

[bponomarenko]

This PR is fixing #408.

preserveDirectiveContent is false by default to remain backward compatibility. In the future (if there will be demand for it) it can be set to true by default, but that would be a breaking change.

Documentation is also updated in vuepress folder as it seems to contain actual docs.

[codecov-io]

Codecov Report

Merging #495 into dev will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev     #495      +/-   ##
==========================================
+ Coverage   96.69%   96.71%   +0.01%     
==========================================
  Files           9        9              
  Lines         666      670       +4     
==========================================
+ Hits          644      648       +4     
  Misses         22       22

Impacted Files	Coverage Δ
src/mixin.js	96.66% <100%> (+0.05%)	⬆️
src/index.js	99.64% <100%> (ø)	⬆️
src/directive.js	92.98% <100%> (+0.25%)	⬆️

---

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[codecov-io]

Codecov Report

Merging #495 into dev will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev     #495      +/-   ##
==========================================
+ Coverage   96.69%   96.71%   +0.01%     
==========================================
  Files           9        9              
  Lines         666      670       +4     
==========================================
+ Hits          644      648       +4     
  Misses         22       22

Impacted Files	Coverage Δ
src/mixin.js	96.66% <100%> (+0.05%)	⬆️
src/index.js	99.64% <100%> (ø)	⬆️
src/directive.js	92.98% <100%> (+0.25%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update aa20962...2dd3c53. Read the comment docs.

[bponomarenko]

Happy New Year @kazupon!
Does this PR make sense?

[kazupon]

Good job! 👍
Thanks!

[bponomarenko]

Perfect! Thanks for merging.

[sirlancelot]

Thanks for this! 🎉 I understand making it false for backwards compatibility but I feel like true should be the default in a future release.