Issue with the DIRECTORY.md script

[dlesnoff]

@ZoomRmc proposed a script to automatically fetch the names of the different algorithms implementations.
This script does not detect the catalan_numbers.nim file in the dynamic programming directory.
I would accept any PR that partially fix these algorithm's detection issues.

[ZoomRmc]

The script assumes implementations conform to the regular Nim module format, with the description being Doc comments. I wanted to mention on your PR, but got distracted.

I propose we just add the requirement to the guidelines.

The script should fall back on the file name to get the title in case it can't be read from the first line. I'll check it a bit later.

[ZoomRmc]

I've checked and can't reproduce. All files are detected, including the scripts directory, which I'm adding to a list of ignored sub dirs in a follow-up PR.

[ZoomRmc]

Here's the output after changes made in #15:

⚠: "dynamic_programming\catalan_numbers.nim". First line is not a doc comment! Deriving title from a file name.
⚠: "dynamic_programming\viterbi.nim". First line is not a doc comment! Deriving title from a file name.
<!--- DO NOT EDIT: This file is automatically generated by `directory.nim` -->

# The Algorithms — Nim: Directory Hierarchy

## Dynamic Programming
  * [Catalan Numbers](dynamic_programming/catalan_numbers.nim)
  * [Viterbi](dynamic_programming/viterbi.nim)

## Strings
  * [Check Anagram](strings/check_anagram.nim)

First two lines are written to standard error stream.

[dlesnoff]

I could not reproduce the issue on my desktop, I have to investigate this a little on my laptop.
Thank you for the PR, I will merge this tomorrow. Ping me if I forget.