Fix backtick handling inside tables

Fix https://github.com/markdown-it/markdown-it/issues/303

lib/rules_block/table.js

@@ -25,13 +25,22 @@ function escapedSplit(str) {
   ch  = str.charCodeAt(pos);
 
   while (pos < max) {
-    if (ch === 0x60/* ` */ && (escapes % 2 === 0)) {
+    if (ch === 0x60/* ` */) {
-      backTicked = !backTicked;
+      if (backTicked) {
+        // make \` close code sequence, but not open it;
+        // the reason is: `\` is correct code block
+        backTicked = false;
+        lastBackTick = pos;
+      } else if (escapes % 2 === 0) {
+        backTicked = true;
         lastBackTick = pos;
+      }
     } else if (ch === 0x7c/* | */ && (escapes % 2 === 0) && !backTicked) {
       result.push(str.substring(lastPos, pos));
       lastPos = pos + 1;
-    } else if (ch === 0x5c/* \ */) {
+    }
+
+    if (ch === 0x5c/* \ */) {
       escapes++;
     } else {
       escapes = 0;

test/fixtures/markdown-it/tables.txt

@@ -400,6 +400,53 @@ Another complicated backticks case
 </table>
 .
 
+`\` in tables should not count as escaped backtick
+.
+# | 1 | 2
+--|--|--
+x | `\` | `x`
+.
+<table>
+<thead>
+<tr>
+<th>#</th>
+<th>1</th>
+<th>2</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>x</td>
+<td><code>\</code></td>
+<td><code>x</code></td>
+</tr>
+</tbody>
+</table>
+.
+
+Tables should handle escaped backticks
+.
+# | 1 | 2
+--|--|--
+x | \`\` | `x`
+.
+<table>
+<thead>
+<tr>
+<th>#</th>
+<th>1</th>
+<th>2</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>x</td>
+<td>``</td>
+<td><code>x</code></td>
+</tr>
+</tbody>
+</table>
+.
 
 Should be parsed before code blocks:
 .