Added Not() criterion modifier

examples

```go
bolthold.Where("Category").Not().In("food", "animal")
bolthold.Where("Tags").Not().IsNil()
bolthold.Where("Tags").Not().IsNil().And("Name").Not().RegExp(regexp.MustCompile("ea"))
bolthold.Where(bolthold.Key).Not().Eq(testData[4].Key)
bolthold.Where("Category").Not().Eq("food").And("Category").Not().Eq("animal").Index("Category")

```

We now unfortunately have an overlap with the `Ne()` and `Not().Eq()`,
but it's not worth dropping the `Ne` operator and breaking backwards
compatibility.

.gitignore

@@ -22,3 +22,4 @@ _testmain.go
 *.exe
 *.test
 *.prof
+*.swp

find_test.go

@@ -303,7 +303,7 @@ var testResults = []test{
 			field := ra.Field()
 			_, ok := field.(string)
 			if !ok {
-				return false, fmt.Errorf("Field not a string, it's a %T!", field)
+				return false, fmt.Errorf("field not a string, it's a %T", field)
 			}
 
 			return strings.HasPrefix(field.(string), "oat"), nil
@@ -316,7 +316,7 @@ var testResults = []test{
 			record := ra.Record()
 			_, ok := record.(*ItemTest)
 			if !ok {
-				return false, fmt.Errorf("Record not an ItemTest, it's a %T!", record)
+				return false, fmt.Errorf("record not an ItemTest, it's a %T", record)
 			}
 
 			return strings.HasPrefix(record.(*ItemTest).Name, "oat"), nil
@@ -435,7 +435,7 @@ var testResults = []test{
 			field := ra.Field()
 			_, ok := field.(string)
 			if !ok {
-				return false, fmt.Errorf("Field not a string, it's a %T!", field)
+				return false, fmt.Errorf("field not a string, it's a %T", field)
 			}
 
 			return !strings.HasPrefix(field.(string), "veh"), nil
@@ -448,7 +448,7 @@ var testResults = []test{
 			field := ra.Field()
 			_, ok := field.(string)
 			if !ok {
-				return false, fmt.Errorf("Field not a string, it's a %T!", field)
+				return false, fmt.Errorf("field not a string, it's a %T", field)
 			}
 
 			return !strings.HasPrefix(field.(string), "veh"), nil
@@ -491,6 +491,37 @@ var testResults = []test{
 		query:  bolthold.Where("Category").Eq("food").Index("Category").And(bolthold.Key).Gt(testData[10].Key),
 		result: []int{12, 15},
 	},
+	test{
+		name:   "Not In",
+		query:  bolthold.Where("Category").Not().In("food", "animal"),
+		result: []int{0, 1, 3, 6, 11},
+	},
+	test{
+		name:   "Not IsNil",
+		query:  bolthold.Where("Tags").Not().IsNil(),
+		result: []int{4, 7, 10, 12, 15},
+	},
+	test{
+		name:   "Multiple Not criteria",
+		query:  bolthold.Where("Tags").Not().IsNil().And("Name").Not().RegExp(regexp.MustCompile("ea")),
+		result: []int{4, 7, 10, 15},
+	},
+	test{
+		name:   "Not Equal Key with not modifier",
+		query:  bolthold.Where(bolthold.Key).Not().Eq(testData[4].Key),
+		result: []int{0, 1, 2, 3, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16},
+	},
+	test{
+		name:   "Double Negative", // don't do this, it's confusing
+		query:  bolthold.Where(bolthold.Key).Not().Not().Eq(testData[4].Key),
+		result: []int{4},
+	},
+	test{
+		name: "Not on Index",
+		query: bolthold.Where("Category").Not().Eq("food").And("Category").Not().Eq("animal").
+			Index("Category"),
+		result: []int{0, 1, 3, 6, 11},
+	},
 }
 
 func insertTestData(t *testing.T, store *bolthold.Store) {
@@ -861,7 +892,7 @@ func TestKeyMatchFunc(t *testing.T) {
 			field := ra.Field()
 			_, ok := field.(string)
 			if !ok {
-				return false, fmt.Errorf("Field not a string, it's a %T!", field)
+				return false, fmt.Errorf("field not a string, it's a %T", field)
 			}
 
 			return strings.HasPrefix(field.(string), "oat"), nil

index.go

@@ -288,7 +288,7 @@ func newIterator(tx *bolt.Tx, typeName string, query *Query) *iterator {
 // however if there is only one critrion and it is either > = or >= then we can seek to the value and
 // save reads
 func seekCursor(cursor *bolt.Cursor, criteria []*Criterion) (key, value []byte) {
-	if len(criteria) != 1 {
+	if len(criteria) != 1 || criteria[0].negate {
 		return cursor.First()
 	}
 

query.go

@@ -76,6 +76,7 @@ type Criterion struct {
 	operator int
 	value    interface{}
 	inValues []interface{}
+	negate   bool
 }
 
 func hasMatchFunc(criteria []*Criterion) bool {
@@ -324,6 +325,12 @@ func (c *Criterion) IsNil() *Query {
 	return c.op(isnil, nil)
 }
 
+// Not will negate the following critierion
+func (c *Criterion) Not() *Criterion {
+	c.negate = !c.negate
+	return c
+}
+
 // MatchFunc is a function used to test an arbitrary matching value in a query
 type MatchFunc func(ra *RecordAccess) (bool, error)
 
@@ -449,7 +456,8 @@ func matchesAllCriteria(criteria []*Criterion, value interface{}, encoded bool,
 		if err != nil {
 			return false, err
 		}
-		if !ok {
+
+		if criteria[i].negate == ok {
 			return false, nil
 		}
 	}
@@ -496,6 +504,9 @@ func (q *Query) String() string {
 
 func (c *Criterion) String() string {
 	s := ""
+	if c.negate {
+		s += "NOT "
+	}
 	switch c.operator {
 	case eq:
 		s += "=="