[RFC] Archive Extensions and Mimes

• I have summed up the feature in concise words in the Summary section.
• I have completely described the feature in the Description section.

Summary

We should host archive extensions in a better way.

Description

Currently, all archives are served with the .gz extension, but they're served with Content-Type: text/plain and Content-Encoding: gzip, which makes the .gz extension quite senseless.

We should modify how we treat archives depending on:

• Request path
  • Requested .gz extension
    • Content-Type: application/gzip
    • No Content-Encoding
  • Requested .json extension
    • Content-Type: application/json
    • Content-Encoding: gzip
  • Requested .txt extension
    • Content-Type: text/plain
    • Content-Encoding: gzip

Additionally, we may want to utilize the Content-Type and Accept-Encoding request headers.

Examples:

curl https://aur.archlinux.org/packages.gz
# application/gzip archive is downloaded with no decompression

curl --compressed https://aur.archlinux.org/packages.txt
# text/plain decompressed archive is downloaded over `gzip` encoded transport

curl https://aur.archlinux.org/packages-meta-v1.json.gz
# application/gzip archive is downloaded with no decompression

curl --compressed https://aur.archlinux.org/packages-meta-v1.json
# application/json decompressed archive is downloaded over `gzip` encoded transport

At this time, we have no other routes within aurweb which use the .gz, .json or .txt extensions, so this should be safe to use on AUR website.