Convert gist frames to block code

[miry]

Manage to detect gist and download content inside block.
Example of gist https://gist.githubusercontent.com/miry/d7e8a19eb66734fb69cf8ee4c32095bc:

  ` ` `
  #!/usr/bin/env bash

  medup -u miry -d ./posts/miry          # Articles written by miry
  medup @miry -d ./posts/miry            # Alternative way to get articles written by miry
  medup -u miry -d ./posts/favorites -r  # Favorite articles of miry (clapped one)
  medup -u miry -d ./posts/miry --update # Update existing exported posts with latest versions of posts
  medup -u miry -d ./posts/miry --assets-images  # Save images to assets folder
  medup -p jetthoughts -d ./posts/jetthoughts # Export Jetthought publication's posts
  medup jetthoughts -d ./posts/jetthoughts # Alternative way to export Jetthought publication's posts
  medup https://medium.com/notes-and-tips-in-full-stack-development/medup-backups-articles-8bf90179b094 # Export single article
  medup https://jtway.co/git-minimum-for-effective-project-development-841a0b865ef0 # Export signle article with custom domain
  ` ` `
  [usage.sh view raw](https://gist.githubusercontent.com/miry/d7e8a19eb66734fb69cf8ee4c32095bc/raw/a577b9fc77074f182b16f869035c81a174542399/usage.sh)