Allow file list as input

[rien333]

cat allows you to print multiple files:

$ cat file1.txt file2.txt ...
# file 1 output
# file 2 output
...

Would be cool if mdcat would be compatible with cat in this way. A neat addition of this feature would be that you can cat files that adhere to a regex pattern, so you can for example cat all notes pertaining to some author:

$ mdcat Smith*.md

[swsnr]

I’ll merge a pull request which adds this feature.

[tsonev7]

@lunaryorn are you still doing this? :)
I can take this task if you don't have time to implement it.

[swsnr]

I never said that I would do this.

If anyone wants this they’ll have to make a pull request.