Added close to complete skeleton boss

See merge request !36

Massive rework of inventory system.

See merge request !35

- Now has 4 sections.
- Made to support the new inventory design.
- Passive items now only affect player if added to specific sections.
- All sections have their full size, null indicates a slot is empty.
- Functionality to easily move items between sections.
- Much more convoluted back-end code.
- It just works now.

Dodge

See merge request !34

Updating master branch.

See merge request !33

util bar merge

See merge request !32

Mana and stamina.

See merge request !31

Improvements to attacks.

See merge request !30