Version 0.2.4: bugs fixed... and added

A few additions:

• BUGS! Specifically, bug creatures that follow a fixed patrol route between two points that (currently) kill on touch, but can be killed by jumping on them.
• BUGS! Specifically, removed the occasional event where you could keep jumping in mid-air -- effectively flying -- instead of doing only one double-jump before having to come back to land again.
• New dashboard! Decided to reserve the bottom of the screen for a dashboard that includes information like current level name, the keys you've collected. There's spaces set aside for health (the hearts) and shields, for a future health system (so the bugs only hurt you, not outright kill you).
• Spikes! Added spike traps that kill you on touch.
• Tutorial! Two new tutorial levels, one for the spikes and one for the bugs.
• Refactor! Some behind-the-scenes work, refactoring some of the code and reorganising the Godot project so it's easier to find things.

Next steps is to implement the health system as described above, and hooking that into the dashboard.