Lyra colorscheme for vim

Configuration options:

g:lyra_use_system_colors
- v:true: Only use terminal colors 0-15
- v:false: Uses 256 colors or truecolor if available
g:lyra_transparent
- v:true: Background is cleared to NONE
- v:false: Background is cleared to theme color
g:lyra_no_highlighting
- v:true: Minimal colorscheme, only comments are colored
- v:false: Use full colorscheme
g:lyra_string_bg
- v:true: Strings have a different background color
- v:false: Strings don't set a background color