Add public API function to get Nord colors (#224)

Implemented the `NordPalette` pubic API function that returns all Nord
colors as dictionary. This allows to use the colors in other Vim scripts
without the need to copy & paste the colors from the documentations or
the Nord Vim theme sources.

Co-authored-by: Arctic Ice Studio <development@arcticicestudio.com>
Co-authored-by: Sven Greb <development@svengreb.de>

Closes GH-224

colors/nord.vim

@@ -772,3 +772,17 @@ hi! link VimwikiList markdownListMarker
 " YAML
 " > stephpy/vim-yaml
 call s:hi("yamlKey", s:nord7_gui, "", s:nord7_term, "", "", "")
+
+"+------------+
+"+ Public API +
+"+------------+
+"+--- Functions ---+
+
+function! NordPalette() abort
+  let ret = {}
+  for color in range(16)
+    execute 'let ret["nord'.color.'"] = s:nord'.color.'_gui'
+  endfor
+  let ret["nord3_bright"] = s:nord3_gui_bright
+  return ret
+endfunction