Adds the language capability for component level attributes, implementing #299.

Currently adds one attribute, slow_fsms=n telling the compilation pass to use slow counter based FSMs with N states per count. Requires that n divides the II of the component.

This currently has a few implementation details and limitations that need to be discussed:

• This is only available at the component level, so this does not allow us to generate different types of FSMs for different events.
• The delay of a slow FSM must divide the II of the event (in multi event components this means it must divide the GCD), there is not a really nice way to detect this sort of issue.
• 0 is currently used to specify simple FSMs.
• The attribute is now added automatically by a pass rather than decided at compile time, which subscribes it to the same limitations as everything else.

As a proof of concept, this also adds the #[counter_fsm] attribute, which allows the user to specify whether an attribute instantiates a counter fsm or not.