Having so much the logic and lambdas in main() was getting unwieldy.
Moving it into a class simplifies this, and also opens up a path
towards supporting "Open in New Window" :^)
This adds storage for cookies that maye be set via 'document.cookie' in
JavaScript or the Set-Cookie HTTP header. For now, it parses only the
name-value pair from a set-cookie line, but does not parse optional
attributes.
Currently, storage is ephemeral and only survives for the lifetime of
the Browser instance.
