refactor(api): handle option dicts properly

Do not copy a lot of lua strings (dict keys) to just strequal() them
Just compare them directly to a dedicated hash function.

feat(generators): HASHY McHASHFACE

test/functional/api/command_spec.lua

@@ -21,7 +21,7 @@ describe('nvim_get_commands', function()
   it('validates input', function()
     eq('builtin=true not implemented', pcall_err(meths.get_commands,
       {builtin=true}))
-    eq('unexpected key: foo', pcall_err(meths.get_commands,
+    eq("Invalid key: 'foo'", pcall_err(meths.get_commands,
       {foo='blah'}))
   end)