Add 'recursive_search' option to do recursive search for the given folder

[ingjieye]

[Acidham]

did you run performance test with 100,200,1000 notes?

i tried recursive search and performance loss was huge.

[ingjieye]

I have 70 markdown files with ~4000 lines, and it works perfectly. BTW It's not recursively listing files inside a given folder impact the performance but the number of files, so adding this feature really has nothing to do with performance impact I think.