Add woff2 encoder/decoder support for overlapSimpleBitmap.

overlapSimpleBitmap is a new field in the transformed glyf table (https://www.w3.org/TR/WOFF2/#glyf_table_format). It allows the overlap simple flag set on glyphs in the original font to be saved into the woff2 encoding.

src/woff2_enc.cc

@@ -28,13 +28,9 @@
 
 namespace woff2 {
 
+
 namespace {
 
-
-using std::string;
-using std::vector;
-
-
 const size_t kWoff2HeaderSize = 48;
 const size_t kWoff2EntrySize = 20;
 
@@ -183,7 +179,7 @@ size_t MaxWOFF2CompressedSize(const uint8_t* data, size_t length) {
 }
 
 size_t MaxWOFF2CompressedSize(const uint8_t* data, size_t length,
-    const string& extended_metadata) {
+                              const std::string& extended_metadata) {
   // Except for the header size, which is 32 bytes larger in woff2 format,
   // all other parts should be smaller (table header in short format,
   // transformations and compression). Just to be sure, we will give some