fix(CLI): request value cursor handling and docs

* now the cursor will only be set permanently if the -r flag is used in
  'cursor' mode. In 'cursor=value' mode, the cursor change doesn't
  persist among the flags. That way, one can easily distinguish
  between setting the cursor, and setting a field. However,
  '...sublevel.level=value' will still work as it did previously, yet
  the cursor change will not persist.
* Documentation was adjusted to represent the new cursor style.

Fixes #86

src/mako/api/lib/rbuild.mako

@@ -95,6 +95,9 @@ impl${rb_params} ${ThisType} {
     % endfor
     % endif
     pub fn ${mangle_ident(a)}${type_params}(&self${method_args}) -> ${RType}${mb_tparams} {
+        % if part_prop and request_value:
+        let parts = ${mangle_ident(REQUEST_VALUE_PROPERTY_NAME)}.to_parts();
+        % endif
         ${RType} {
             hub: self.hub,
             % for p in required_props:
@@ -102,7 +105,7 @@ impl${rb_params} ${ThisType} {
             % endfor
             ## auto-generate parts from request resources
             % if part_prop and request_value:
-            ${property(part_prop.name)}: ${mangle_ident(REQUEST_VALUE_PROPERTY_NAME)}.to_parts(),
+            ${property(part_prop.name)}: parts,
             % endif
             % for p in optional_props:
             ${property(p.name)}: Default::default(),