add parsley entity that enables read command

data/entities.yaml

@@ -330,6 +330,33 @@
     ignition: 0.1
     duration: [20, 40]
     product: ash
+- name: parsley
+  display:
+    attr: plant
+    char: 'p'
+  description:
+    - A fast-growing plant with a pungent aroma, often found growing
+      near rocks.
+    - |
+      When equipped as a device, parsley enables the `read`
+      command, which can be used to turn text into values:
+      ```
+      read : Text -> (Unit + a)
+      ```
+      If the given `Text`{=type} represents a value of the expected
+      type, the value will be returned wrapped in `inr`; otherwise
+      `inl ()` is returned.  For example:
+    - |
+      ```
+      (read "3" : Unit + Int) == inr 3
+      ```
+      but
+      ```
+      (read "hello" : Unit + Int) == inl ()
+      ```
+  properties: [pickable, growable]
+  capabilities: [read]
+  growth: [10, 100]
 - name: linotype
   display:
     attr: silver

data/worlds/classic.world

@@ -75,6 +75,7 @@ overlay
     [ {stone}
     , mask (hash % 10 == 0) {stone, rock}
     , mask (hash % 100 == 0) {stone, lodestone}
+    , mask (hash % 300 == 0) {grass, parsley}
     ]
   )
 , mask (big && soft && natural)