Multiline strings can't end with "\"

i.e. this is valid:

	key = """ foo \
	"""

But this is not:

	key = """ foo \ """

Fixes #322

parse.go

@@ -220,7 +220,7 @@ func (p *parser) value(it item, parentIsArray bool) (interface{}, tomlType) {
 	case itemString:
 		return p.replaceEscapes(it, it.val), p.typeOfPrimitive(it)
 	case itemMultilineString:
-		return p.replaceEscapes(it, stripFirstNewline(stripEscapedNewlines(it.val))), p.typeOfPrimitive(it)
+		return p.replaceEscapes(it, stripFirstNewline(p.stripEscapedNewlines(it.val))), p.typeOfPrimitive(it)
 	case itemRawString:
 		return it.val, p.typeOfPrimitive(it)
 	case itemRawMultilineString:
@@ -647,7 +647,7 @@ func stripFirstNewline(s string) string {
 }
 
 // Remove newlines inside triple-quoted strings if a line ends with "\".
-func stripEscapedNewlines(s string) string {
+func (p *parser) stripEscapedNewlines(s string) string {
 	split := strings.Split(s, "\n")
 	if len(split) < 1 {
 		return s
@@ -679,6 +679,10 @@ func stripEscapedNewlines(s string) string {
 			continue
 		}
 
+		if i == len(split)-1 {
+			p.panicf("invalid escape: '\\ '")
+		}
+
 		split[i] = line[:len(line)-1] // Remove \
 		if len(split)-1 > i {
 			split[i+1] = strings.TrimLeft(split[i+1], " \t\r")

toml_test.go

@@ -299,8 +299,6 @@ func TestToml(t *testing.T) {
 				"invalid/inline-table/add",
 				"invalid/table/duplicate-key-dotted-table",
 				"invalid/table/duplicate-key-dotted-table2",
-
-				"invalid/string/multiline-bad-escape-3", // https://github.com/BurntSushi/toml/issues/322
 			},
 		}