Fix html entities: support \<entity>{} and prevent partial replacements

org/testdata/inline.pretty_org

@@ -51,3 +51,6 @@
   - [[example_interpolate_h:tag value with specical chars % : &]] (w/o tag [[example_interpolate_h]])
 - =#+MACROs=: {{{headline(yolo)}}}
   #+MACRO: headline @@html:<h1>$1</h1>@@
+- org entities
+  - =\pi= & =\pi{}= => \pi & \pi{}
+  - =\angle{}= & =\angle= & =\ang= =>= \angle{} \angle \ang