Support upper case MD extension

[danintel]

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The RE \.(?:markdown|mdown|mkdn|md|mkd|mdwn|mdtxt|mdtext|text)(?:#.*|\?.*)?$ does not support .MD. I modified it as follows and it worked: \.(?:markdown|mdown|mkdn|md|MD|mkd|mdwn|mdtxt|mdtext|text)(?:#.*|\?.*)?$

[simov]

That's a good point. I wonder what is the performance difference between case sensitive and case insensitive regex in this case. I might have to make a few tests.

[danintel]

I don't know. An alternative is to copy the string and convert to lower case--for comparison purposes only.