v0.3 Saving, QoL features

This update is entirely based around QoL features like saving and loading, being able to multi-task while battling, and fixing some annoying bugs.

[Changes/Updates]

• Saving/loading are now working. However, at this time your save will not carry over between versions. This may change in the future but likely not.
• Challenges now take you directly to the challenge that was completed. 
  • There is currently a bug that may require you to press the button a second time to take you directly to the challenge.
• You can now do gear upgrades, shop, upgrade skills, and complete challenges while battling.
  • The game has been re-balanced around this change. It was originally balanced for faster progression enemy to enemy but now is slowed a bit since you can make upgrades on the fly.
• Rewards for challenges have been re-balanced for more variety.
• Currency upgrade stat now displays correctly.
• General gear balancing.
• Buffed the speed stat to make it a more enticing option. 
  • Still evaluating the sweet spot to make this desirable.
• Fixed an issue where some stats were not being calculated correctly.
• Enemy reward balancing.

[Known Bugs]

• Loading Game allows you to press it with no previous save file, however this will start a new game like normal.
• The speed stat displayed for challenges doesn't show the time but the numerical value used in calculations. It is still calculated correctly and will be available to claim under the given conditions.
• You cannot view the item screen while battling. Currently every screen an item is displayed on shows you how many you own. This button/screen may be removed entirely as it feels a bit redundant.
• You may have to press the Challenges button twice in order to go directly to the challenge that can be claimed.

[Future Additions]

• The next version is planned to have at least one new area but I'm shooting for two and new gear to go along with those areas. I would like a total of 5 areas.
• Possibly an unexpected ending that hints at something I have an idea for.
• I no longer plan on adding an arena mode. I have another project I'd like to invest my time into after this one.
• A tip screen to help guide players along in the place of an active tutorial.
• A font color change to several numerical values to make them stand out.