Indicate error/warning origin

[herrvonvoid]

Please add a prefix to error messages that tells users where the error is coming from!

For example the nvim-lspconfig is missing error took me quite some time to track down, where it's coming from. I would be awesome if the error would read "Neoconf: nvim-lspconfig not installed?".

Since we're already talking about it: please note in the README install instructions that there is a default (but optional) dependency on nvim-lspconfig. It could read something like:

use({
  "folke/neoconf.nvim",
  -- if plugins.lspconfig.enabled = true (default):
  requires = 'neovim/nvim-lspconfig'
})