Lex performance improvement (#176)

* Use []token instead of chan token

name             old time/op    new time/op    delta
ParseToml-8        1.18ms ± 0%    0.91ms ± 0%  -22.98%
UnmarshalToml-8    1.29ms ± 0%    0.95ms ± 0%  -25.96%

name             old alloc/op   new alloc/op   delta
ParseToml-8         429kB ± 0%     444kB ± 0%   +3.49%
UnmarshalToml-8     451kB ± 0%     466kB ± 0%   +3.32%

name             old allocs/op  new allocs/op  delta
ParseToml-8         14.1k ± 0%     13.7k ± 0%   -2.31%
UnmarshalToml-8     15.1k ± 0%     14.7k ± 0%   -2.16%

* Lex on []byte instead of io.Reader

name             old time/op    new time/op    delta
ParseToml-8        1.18ms ± 0%    0.29ms ± 0%  -75.18%
UnmarshalToml-8    1.27ms ± 0%    0.38ms ± 0%  -70.38%

name             old alloc/op   new alloc/op   delta
ParseToml-8         429kB ± 0%     135kB ± 0%  -68.53%
UnmarshalToml-8     451kB ± 0%     157kB ± 0%  -65.22%

name             old allocs/op  new allocs/op  delta
ParseToml-8         14.1k ± 0%      3.2k ± 0%  -77.20%
UnmarshalToml-8     15.1k ± 0%      4.2k ± 0%  -72.00%

toml.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"runtime"
 	"strings"
@@ -251,8 +252,8 @@ func (t *Tree) createSubTree(keys []string, pos Position) error {
 	return nil
 }
 
-// LoadReader creates a Tree from any io.Reader.
-func LoadReader(reader io.Reader) (tree *Tree, err error) {
+// LoadBytes creates a Tree from a []byte.
+func LoadBytes(b []byte) (tree *Tree, err error) {
 	defer func() {
 		if r := recover(); r != nil {
 			if _, ok := r.(runtime.Error); ok {
@@ -261,13 +262,23 @@ func LoadReader(reader io.Reader) (tree *Tree, err error) {
 			err = errors.New(r.(string))
 		}
 	}()
-	tree = parseToml(lexToml(reader))
+	tree = parseToml(lexToml(b))
+	return
+}
+
+// LoadReader creates a Tree from any io.Reader.
+func LoadReader(reader io.Reader) (tree *Tree, err error) {
+	inputBytes, err := ioutil.ReadAll(reader)
+	if err != nil {
+		return
+	}
+	tree, err = LoadBytes(inputBytes)
 	return
 }
 
 // Load creates a Tree from a string.
 func Load(content string) (tree *Tree, err error) {
-	return LoadReader(strings.NewReader(content))
+	return LoadBytes([]byte(content))
 }
 
 // LoadFile creates a Tree from a file.