Add low-memory option using WPE on Linux

[chase]

Chromium isn't as memory friendly as Firefox or WebKit

Firefox is difficult to embed compared to Servo, but Servo isn't a complete engine

For Linux, Web Platform for Embedded is kind of like CEF, but with WebKit instead

It would probably use the reference graphics backend: https://github.com/Igalia/WPEBackend-fdo

This would be quite a bit of work