pkgs/vim: Add mucomplete plugin

I've been looking for a good, lightweight, and fast completion engine
that also has little or no dependencies. The `mucomplete` plugin seems
to fit the bill as I also don't have any fancy requirements.

pkgs/devhell/vim/default.nix

@@ -18,6 +18,7 @@ pkgs.vim_configurable.overrideAttrs (drv: {
         vim-better-whitespace
         vim-lastplace
         vim-nix
+        vim-mucomplete
         vim-signify
         vim-toml
         colorizer
@@ -51,6 +52,12 @@ pkgs.vim_configurable.overrideAttrs (drv: {
       filetype plugin indent on
       colorscheme tender
 
+      " mucomplete Settings
+      set completeopt+=menuone
+      set completeopt+=noinsert
+      set shortmess+=c
+      set belloff+=ctrlg
+
       " signify Settings
       set updatetime=100