Support relative size specification like (=100%x).

lib/helpers/parse_image_size.js

@@ -13,7 +13,7 @@ function parseNextNumber(str, pos, max) {
 
   code = str.charCodeAt(pos);
 
-  while (pos < max && (code >= 0x30 /* 0 */ && code <= 0x39 /* 9 */)) {
+  while (pos < max && (code >= 0x30 /* 0 */ && code <= 0x39 /* 9 */) || code === 0x25 /* % */) {
     code = str.charCodeAt(++pos);
   }
 

test/fixtures/markdown-it-imsize/imsize.txt

@@ -278,6 +278,11 @@ Coverage. Image
 .
 <p><img src="x" alt="test" width="100" height="200"></p>
 .
+.
+![test](test =100%x)
+.
+<p><img src="test" alt="test" width="100%"></p>
+.
 
 Coverage. Link
 .