add alternative diaeresis order

In some cases, texts encoded with Beta Code represent letters that have
both diaeresis and an accent mark in the order letter + diaeresis +
accent. Currently, only letter + accent + diaeresis is supported.

This change adds mappings from Beta Code to Unicode so that both orders
are supported.

Fixes #5

beta_code_to_unicode.json

@@ -556,10 +556,13 @@
   "I+": "ϊ",
   "I/": "ί",
   "I/+": "ΐ",
+  "I+/": "ΐ",
   "I=": "ῖ",
   "I=+": "ῗ",
+  "I+=": "ῗ",
   "I\\": "ὶ",
   "I\\+": "ῒ",
+  "I+\\": "ῒ",
   "J": "ς",
   "K": "κ",
   "L": "λ",
@@ -596,10 +599,13 @@
   "U+": "ϋ",
   "U/": "ύ",
   "U/+": "ΰ",
+  "U+/": "ΰ",
   "U=": "ῦ",
   "U=+": "ῧ",
+  "U+=": "ῧ",
   "U\\": "ὺ",
   "U\\+": "ῢ",
+  "U+\\": "ῢ",
   "W": "ω",
   "W(": "ὡ",
   "W(/": "ὥ",
@@ -703,10 +709,13 @@
   "i+": "ϊ",
   "i/": "ί",
   "i/+": "ΐ",
+  "i+/": "ΐ",
   "i=": "ῖ",
   "i=+": "ῗ",
+  "i+=": "ῗ",
   "i\\": "ὶ",
   "i\\+": "ῒ",
+  "i+\\": "ῒ",
   "j": "ς",
   "k": "κ",
   "l": "λ",
@@ -743,10 +752,13 @@
   "u+": "ϋ",
   "u/": "ύ",
   "u/+": "ΰ",
+  "u+/": "ΰ",
   "u=": "ῦ",
   "u=+": "ῧ",
+  "u+=": "ῧ",
   "u\\": "ὺ",
   "u\\+": "ῢ",
+  "u+\\": "ῢ",
   "w": "ω",
   "w(": "ὡ",
   "w(/": "ὥ",