test case-insensitivity of entry types and field keys

example/examples.bib

@@ -55,12 +55,12 @@
   indextitle   = {Effect of immobilization on catalytic characteristics},
 }
 
-@article{angenendt,
+@Article{angenendt,
   author       = {Angenendt, Arnold},
   title        = {In Honore Salvatoris~-- Vom Sinn und Unsinn der
                   Patrozinienkunde},
   journaltitle = {Revue d'Histoire Eccl{\'e}siastique},
-  date         = 2002,
+  Date         = 2002,
   volume       = 97,
   pages        = {431--456, 791--823},
   langid       = {german},

src/parser.jl

@@ -89,7 +89,7 @@ field!(parser, dict) = begin
         if token != "}"
             key = token
             expect!(parser, "=")
-            token, dict[key] = value!(parser)
+            token, dict[lowercase(key)] = value!(parser)
         end
     end
     expect(parser, token, "}")