fix README.md
fix Parser constructor
Revert "fix Parser constructor"

This reverts commit 90a936e7790c790db4b9021a05edbf734cbe6902.
fix Constructors: BlockLexer, InlineLexer, Parser
enhancement: change the output format of code blocks
simply use `<pre></pre>` instead of `<pre><code></code></pre>`
add an important comment about fenced code blocks
update the documentation
update
update