make unique fields case-insensitive

src/grung/db.py

@@ -1,4 +1,5 @@
 import inspect
+import re
 from functools import reduce
 from operator import ior
 
@@ -41,7 +42,7 @@ class RecordTable(table.Table):
                 reduce(
                     ior,
                     [
-                        Query().fragment({field.name: document[field.name]})
+                        Query()[field.name].matches(document[field.name], flags=re.IGNORECASE)
                         for field in document._metadata.fields.values()
                         if field.unique
                     ],