Markdown: skip frontmatter area

[masatake]

Ideally, we should run a guest parser on the area.
This time, I make ctags just skip the areas.

[codecov]

Codecov Report

Merging #3031 (e8a56fa) into master (298387a) will decrease coverage by 0.00%.
The diff coverage is 63.63%.

❗ Current head e8a56fa differs from pull request most recent head a679933. Consider uploading reports for the commit a679933 to get more accurate results

@@            Coverage Diff             @@
##           master    #3031      +/-   ##
==========================================
- Coverage   87.32%   87.31%   -0.01%     
==========================================
  Files         199      199              
  Lines       47468    47477       +9     
==========================================
+ Hits        41451    41456       +5     
- Misses       6017     6021       +4     

Impacted Files	Coverage Δ
main/trace.c	80.39% <ø> (ø)
parsers/yaml.c	92.06% <33.33%> (-6.25%)	⬇️
optlib/markdown.c	100.00% <100.00%> (ø)

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[masatake]

@leleliu008, do you have an idea to recover the broken image source of centos6?

[leleliu008]

@masatake

use my latest version of pre-build Python:

curl -LO https://github.com/leleliu008/python-prebuild/releases/download/3.9.5/python-3.9.5-x86_64-linux-glibc.tar.xz
tar xf python-3.9.5-x86_64-linux-glibc.tar.xz -C /opt
export PATH=/opt/python-3.9.5-x86_64-linux-glibc/bin:$PATH

Note: installation dir must be /opt/python-3.9.5-x86_64-linux-glibc.