add b flag to pax

[willpuckett]

This PR adds a b flag to pax to set content type on pdf requests so they display in browser instead of downloading.
I also updated to Deno.serve, and changed the markdown parser since the original one wouldn't load when in testing.

[kawarimidoll]

Thank you for your PR!

• I have never used GitHub to store PDF files, so I don't understand why this feature is needed. Can you give me some examples? Once PDF is supported, many other file types might need to be supported as well, but I don’t want to add a lot of filetype-specific code.
• Please remove .vscode/ directory.
• Please apply deno fmt.

[willpuckett]

Thanks for taking the time to review it! I have found pax to be incredibly useful through the years. I usually use it with Deno, but last week I was consolidating some documentation for my printers. I needed to reference other repos, but I didn't want to use submodules because it was too much information and I just wanted to be able to quickly get to a few files. I made markdown documents with the relevant information. Many links were schematics, which tend to be pdfs. They don't display great in the github pdf viewer—it looks pretty blurry when you zoom in, and it only loads the first few pages. Using the github raw link, github has the headers set for it to download, not open in browser, which then involves navigating and opening the file which is far less streamlined.
This behavior is largely confined to pdfs as far as I can tell. Most other raw files will open in browser, so I don't think it's going to result in substantial bloat. I'm imagining that the behaviour of downloading the file is still preferrable by default, so I added it as a flag.

[willpuckett]

(the markdown link in the above response uses a staging version of pax I put at pux.deno.dev)

[kawarimidoll]

Thank you for responding and fixing codes.
The test failed due to a change in the type of the result of the handleURL, so I'm checking the test implementation.
If there is no problem, I will marge this PR.

[kawarimidoll]

Thank you so much! Nice work!

[willpuckett]

Thanks so much!