Simple neovim plugin to set diagnostic level.

The functions that take level as input can take an integer between 1 and 4 (where 1 is ERROR) or the full vim diagnostic setting level: vim.diagnostic.severity.ERROR.

set_diag_level(level) - Display only messages of this level
set_diag_min(level) - Display only messages with severity >= this level

set_sign_level(level) - Add signs for only this level
set_sign_min(level) - Add signs for diagnostics >= this level

set_underline_level(level) - Underline only for this level
set_underline_min(level) - Underline for >= this level

Add tests!