Benchmark against other libraries (#175)

BenchmarkUnmarshalToml-8             1000  1320117 ns/op  450932 B/op  15072 allocs/op
BenchmarkUnmarshalBurntSushiToml-8   3000   402897 ns/op   82900 B/op   1761 allocs/op
BenchmarkUnmarshalJson-8            20000    66092 ns/op    3536 B/op    101 allocs/op
BenchmarkUnmarshalYaml-8            10000   189600 ns/op   44872 B/op   1058 allocs/op

marshal.go

@@ -268,15 +268,20 @@ func valueFromTree(mtype reflect.Type, tval *Tree) (reflect.Value, error) {
 			mtypef := mtype.Field(i)
 			opts := tomlOptions(mtypef)
 			if opts.include {
-				key := opts.name
-				exists := tval.Has(key)
-				if exists {
+				baseKey := opts.name
+				keysToTry := []string{baseKey, strings.ToLower(baseKey), strings.ToTitle(baseKey)}
+				for _, key := range keysToTry {
+					exists := tval.Has(key)
+					if !exists {
+						continue
+					}
 					val := tval.Get(key)
 					mvalf, err := valueFromToml(mtypef.Type, val)
 					if err != nil {
 						return mval, formatError(err, tval.GetPosition(key))
 					}
 					mval.Field(i).Set(mvalf)
+					break
 				}
 			}
 		}