Add right prompt support (zsh and fish)

[thecaralice]

• Closes #23.
• Changed $SILVER to $SILVER_LEFT, $SILVER_SEPARATOR to $SILVER_LEFT_SEPARATOR etc., also silver print is now silver lprint
• For bash, zsh and fish edited init files for backwards compatibility.
• Prompts can be empty now
• Only supports Powershell 7.x

TODO:

• [x] Edit powershell script to get backwards support
  • [x] Check Windows support
• [x] Refactor to remove code duplicated in print functions
• [x] Update readme.md
  • [x] Change variables to the new ones
  • [x] Include information about right prompt
• [x] Update wiki Updated wiki is on https://github.com/MinerChAI/silver-wiki/tree/rprompt

[thecaralice]

Working with conflicts resolved, ready to merge

[thecaralice]

Merged wiki