Reduce warning spam

[jdm]

Two of the most common warnings I see reported in Servo's automatic reporting system are stop_parsing not implemented, full speed ahead! and FIXME: /script> not fully implemented. We should investigate what those mean and remove them if they're not actually useful.

[jdm]

https://github.com/servo/html5ever/blob/d4cd4d4598a2e6f00519e1bc8b1f80100a4407c6/src/tree_builder/rules.rs#L795

[jdm]

https://github.com/servo/html5ever/blob/d4cd4d4598a2e6f00519e1bc8b1f80100a4407c6/src/tree_builder/actions.rs#L170

[Ygg01]

The </script> warning was tied to issues #7 #19.

As for stop_parsing, I assume that since it's this rule and from what I can tell, it depends on hooking into Servo so JS can write stuff.

[nox]

</script> has been taken care of. Will look into stop_parsing.

[nox]

I'm pretty sure stop_parsing is useless now, will clean up.