Grid of Yendor QoL update

Just a minor quality-of-life update based on feedback from the jam and in the comments:

• Implemented Excel-like keybinds for moving, i.e. (Shift+)Tab/Enter
• Marked bosses with purple highlight/text
• Made typing more responsive, especially after moving
• Made background cells darker
• Reduced difficulty, especially in later levels

The jam version of the game should still be downloaded for rating purposes. These files are marked with "jam-rating".

What's coming next:

• Difficulty select
• More animations/sounds
• Graphics/sound options
• Better level generation
• Better dialogue system