Provide a wide range of converters for VSGI

[arteymix]

VSGI should provide a wide range of converters adapted for web development requirements.

• base64 encoding
• dechunking requests
• url encoding
• quoted printable

[arteymix]

The only supported codings by the HTTP/1.1 protocol are: chunked, gzip, compress, deflate and identity and they are already covered by GLib.

The only missing converter is a dechunker.

[arteymix]

In short, there's a few things to implement:

• compressor and decompressor for compress and br (Brotli)
• dechunker with Decode chunked encoding #106

MDN has a list of content codings: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Encoding

[arteymix]

We could support many compression format using squash.