Added right prompt support (fish and zsh)

[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 (needs also powershell). Also prompts can be empty now

TODO:

• [x] Edit powershell script to get backwards support
  • [x] Check Windows support
• [x] Refactor to remove code duplicated in print functions
• [ ] Update readme.md
  • [x] Change variables to the new ones
  • [ ] Include information about right prompt
• [ ] Update wiki
• [ ] Update Cargo.toml

[thecaralice]

Right prompt is working now, needs documentation updates. GitHub doesn't have support for wiki PR's so I con't edit it.

[thecaralice]

Note: Powershell script only works on Powershell Core 7+

[thecaralice]

Closing to change the source branch