Add different classes to hocr output depending on BlockType

These classes are taken from the hOCR specification, and seem
to map well onto the BlockType types. There are probably more that
could be added.

src/api/hocrrenderer.cpp

@@ -209,8 +209,21 @@ char* TessBaseAPI::GetHOCRText(ETEXT_DESC* monitor, int page_number) {
       AddBoxTohOCR(res_it.get(), RIL_PARA, hocr_str);
     }
     if (res_it->IsAtBeginningOf(RIL_TEXTLINE)) {
-      hocr_str << "\n     <span class='ocr_line'"
-               << " id='"
+      hocr_str << "\n     <span class='";
+      switch (res_it->BlockType()) {
+        case PT_HEADING_TEXT:
+          hocr_str << "ocr_header";
+          break;
+        case PT_PULLOUT_TEXT:
+          hocr_str << "ocr_textfloat";
+          break;
+        case PT_CAPTION_TEXT:
+          hocr_str << "ocr_caption";
+          break;
+        default:
+          hocr_str << "ocr_line";
+      }
+      hocr_str << "' id='"
                << "line_" << page_id << "_" << lcnt << "'";
       AddBoxTohOCR(res_it.get(), RIL_TEXTLINE, hocr_str);
     }