Automatically create a file or smartly send the data to stdout when piped

[caribpa]

Hi there!

I've been using this little tool lately and I wanted to contribute with some user-friendly improvements:

• Automatically create a file named after the URL/file-path (closes #35) by default
• Or smartly send the data to stdout if the output is being piped
• Force the output to stdout with --output - following the POSIX conventions (guideline 13)
• Add some error handling and show concise error messages

In a nutshell:

$ capture-website https://github.com/git               # Auto-creates github.com-git.png in current dir

$ capture-website https://goo.gl | open -f -a Preview  # Automatically pipes the data

$ echo "<h1>Unicorn</h1>" | capture-website            # Auto-creates stdin.png

$ capture-website /path/to/file.html --type=jpeg       # Auto-creates file.jpeg

$ capture-website file:///path/to/file.html            # Auto-creates path-to-file.html.png

$ capture-website file.html --output test.png          # Auto-creates test.png

$ capture-website file.html --output=-                 # Send the data to stdout

$ capture-website http://i.dont/exist                  # Gracefully exits with an error message

Let me know what you think 😊