[Request] Add highlight groups for Neovim LSP

[srafi1]

Neovim v0.5.0 includes built-in language server protocol (LSP) support and this colorscheme does not have relevant highlight groups for it. I understand that adding highlight groups for every new plugin/feature that comes along would be unwieldy, but considering the fact that this will be included as a core part of Neovim, I think it is worth adding.

These are the relevant groups:

LspDiagnosticsDefaultHint       
LspDiagnosticsDefaultError      
LspDiagnosticsDefaultWarning    
LspDiagnosticsDefaultInformation

In the meantime I have the following set as a workaround:

highlight! link LspDiagnosticsSignError Exception
highlight! link LspDiagnosticsSignWarning WarningMsg