add themes

[Geezus42]

Description

Adding additional themes, mainly more Gruvbox variants.

Theme Submission Checklist

• Included theme in iTerm2 format
• Included 600x300 screenshot, 13pt Monaco font, no transparency
• Updated README.md with new theme and screenshot
• Updated CREDITS.md with new theme
• Ran tools/gen.py to generate themes in all formats
• Updated screenshots/README.md with new theme

[mbadolato]

Hi, thanks for the submission.

• The screenshots for Gruvbox Dark, Gruvbox Material Dark and Hactober are missing,
• The credits lists Gruvbox Material Dark twice and two different authors and is missing the other themes' credits
• The screenshot files are not named correctly
• All of the itermcolors files are names inconsistently, and most incorrectly
• The Readme is missing some links
• The screenshot in gruvbox-material-iterm2.png is not showing the text like the other themes in the repo
• The tools.gen.py was not run to include all other formats

Can you please update? Thanks

[mbadolato]

ping @Geezus42