xiHeaders - modify request headers

This is yet another extension to modify request headers. It stands out by being extremely simple (~100 lines of code).

Rules

Rules are defined as a JSON. Each rule has the following properties:

pattern: the URL pattern this rule applies to. Patterns can include * as a wildcard.
header: the name of the header
value: the new value
action: add|replace|remove [default: replace]
request_types: a list of request types [default: any]

Show reddit images instead of redirecting to a HTML page:

{
  "pattern": "https://i.redd.it/*",
  "header": "Accept",
  "value": "image/*"
}

A similar rule can also be used for i.imgur.com.