Ignore nested STRONGs during rendering

STRONG, in most rendering engines, becomes bold. Bold cannot be applied to
text two times in most languages. This caps the number of times we attempt
to bold text when rendering.

Running `python3 -c 'pad = "_" * 100000; print(pad + "." + pad, end="")' | time ./build/src/cmark-gfm --to $LANG`

Before:

```
./build/src/cmark-gfm --to plaintext > /dev/null  12.29s user 0.00s system 99% cpu 12.321 total
./build/src/cmark-gfm --to commonmark > /dev/null  25.97s user 0.01s system 99% cpu 26.026 total
./build/src/cmark-gfm --to html > /dev/null  0.01s user 0.00s system 43% cpu 0.033 total
./build/src/cmark-gfm --to man > /dev/null  12.91s user 0.00s system 99% cpu 12.938 total
./build/src/cmark-gfm --to latex > /dev/null  13.13s user 0.01s system 99% cpu 13.159 total
```

After:

```
./build/src/cmark-gfm --to plaintext > /dev/null  0.01s user 0.01s system 39% cpu 0.030 total
./build/src/cmark-gfm --to commonmark > /dev/null  0.01s user 0.00s system 41% cpu 0.031 total
./build/src/cmark-gfm --to html > /dev/null  0.01s user 0.00s system 38% cpu 0.030 total
./build/src/cmark-gfm --to man > /dev/null  0.01s user 0.01s system 40% cpu 0.030 total
./build/src/cmark-gfm --to latex > /dev/null  0.01s user 0.00s system 39% cpu 0.033 total
```

Author: gravypod

src/commonmark.c

@@ -189,14 +189,17 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
   // Don't adjust tight list status til we've started the list.
   // Otherwise we loose the blank line between a paragraph and
   // a following list.
-  if (!(node->type == CMARK_NODE_ITEM && node->prev == NULL && entering)) {
-    tmp = get_containing_block(node);
-    renderer->in_tight_list_item =
-        tmp && // tmp might be NULL if there is no containing block
-        ((tmp->type == CMARK_NODE_ITEM &&
-          cmark_node_get_list_tight(tmp->parent)) ||
-         (tmp && tmp->parent && tmp->parent->type == CMARK_NODE_ITEM &&
-          cmark_node_get_list_tight(tmp->parent->parent)));
+  if (entering) {
+    if (node->parent && node->parent->type == CMARK_NODE_ITEM) {
+      renderer->in_tight_list_item = node->parent->parent->as.list.tight;
+    }
+  } else {
+    if (node->type == CMARK_NODE_LIST) {
+      renderer->in_tight_list_item =
+        node->parent &&
+        node->parent->type == CMARK_NODE_ITEM &&
+        node->parent->parent->as.list.tight;
+    }
   }
 
   if (node->extension && node->extension->commonmark_render_func) {
@@ -405,10 +408,12 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     break;
 
   case CMARK_NODE_STRONG:
-    if (entering) {
-      LIT("**");
-    } else {
-      LIT("**");
+    if (node->parent == NULL || node->parent->type != CMARK_NODE_STRONG) {
+      if (entering) {
+        LIT("**");
+      } else {
+        LIT("**");
+      }
     }
     break;
 

src/html.c

@@ -364,10 +364,12 @@ static int S_render_node(cmark_html_renderer *renderer, cmark_node *node,
     break;
 
   case CMARK_NODE_STRONG:
-    if (entering) {
-      cmark_strbuf_puts(html, "<strong>");
-    } else {
-      cmark_strbuf_puts(html, "</strong>");
+    if (node->parent == NULL || node->parent->type != CMARK_NODE_STRONG) {
+      if (entering) {
+        cmark_strbuf_puts(html, "<strong>");
+      } else {
+        cmark_strbuf_puts(html, "</strong>");
+      }
     }
     break;
 

src/latex.c

@@ -385,10 +385,12 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     break;
 
   case CMARK_NODE_STRONG:
-    if (entering) {
-      LIT("\\textbf{");
-    } else {
-      LIT("}");
+    if (node->parent == NULL || node->parent->type != CMARK_NODE_STRONG) {
+      if (entering) {
+        LIT("\\textbf{");
+      } else {
+        LIT("}");
+      }
     }
     break;
 

src/man.c

@@ -225,10 +225,12 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     break;
 
   case CMARK_NODE_STRONG:
-    if (entering) {
-      LIT("\\f[B]");
-    } else {
-      LIT("\\f[]");
+    if (node->parent == NULL || node->parent->type != CMARK_NODE_STRONG) {
+      if (entering) {
+        LIT("\\f[B]");
+      } else {
+        LIT("\\f[]");
+      }
     }
     break;
 

src/plaintext.c

@@ -46,14 +46,17 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
   // Don't adjust tight list status til we've started the list.
   // Otherwise we loose the blank line between a paragraph and
   // a following list.
-  if (!(node->type == CMARK_NODE_ITEM && node->prev == NULL && entering)) {
-    tmp = get_containing_block(node);
-    renderer->in_tight_list_item =
-        tmp && // tmp might be NULL if there is no containing block
-        ((tmp->type == CMARK_NODE_ITEM &&
-          cmark_node_get_list_tight(tmp->parent)) ||
-         (tmp && tmp->parent && tmp->parent->type == CMARK_NODE_ITEM &&
-          cmark_node_get_list_tight(tmp->parent->parent)));
+  if (entering) {
+    if (node->parent && node->parent->type == CMARK_NODE_ITEM) {
+      renderer->in_tight_list_item = node->parent->parent->as.list.tight;
+    }
+  } else {
+    if (node->type == CMARK_NODE_LIST) {
+      renderer->in_tight_list_item =
+        node->parent &&
+        node->parent->type == CMARK_NODE_ITEM &&
+        node->parent->parent->as.list.tight;
+    }
   }
 
   if (node->extension && node->extension->plaintext_render_func) {