Improve interrupt handler layout

[ISSOtm]

• Ensure each "stub" is in its own section, without padding
• Put the STAT handler "inline", since the other handlers are not used
• Put the VBlank handler at $150 so that it can be jr'd to (acceptable because of the header right before)
• Add "dynamic raster FX" STAT handler

[ISSOtm]

See https://gist.github.com/ISSOtm/7a7a082fb2d73b5e7c645e62571b352d for the VBlank handler's skeleton.