Add slope support

[maystey]

The character used to slide down slopes with a low enough incline to be the floor (this is now fixed).

The character used to run up (or slide up if in the Air state) slopes that are too steep to be the floor (this is now fixed).

New bad behavior:

• On slopes with an incline equal to max_floor_angle, the character makes a slight hop after running up and looses their grounding when running down them.
• When the character runs into a steep slope they perform short hops due to sliding upwards. Ideally the player would stay on the ground (no sliding up the slope). This can be exploited to jump higher.

A new ramp obstacle (Rampy) was added to the main Game scene to test the slope behavior.

Closes: #25

Please check if the PR fulfills these requirements:

• [x] The commit message follows our guidelines.
• For bug fixes and features:
  • [x] You tested the changes.
  • [ ] You updated the docs or changelog.

[maystey]

@NathanLovato Thank you very much for your feedback on all of this.

I have a technical question related to pushing further commits. The guidelines state that the commits should be squashed. Should I push further commits to this branch and squash it later, or should I squash it each time before pushing and force it?

[NathanLovato]

I have a technical question related to pushing further commits. The guidelines state that the commits should be squashed. Should I push further commits to this branch and squash it later, or should I squash it each time before pushing and force it?

As you prefer, I can also use the squash and merge feature from GitHub at the end so you don't have to rebase yourself. We have this for the team, as we generate lots of commits.