feat: stricter validation of heading fragments by being Case sensitive

Fixes #8

BREAKING CHANGE: Heading fragments is now Case sensitive.
For example "#ExistIng-Heading" is invalid as it should be "#existing-heading".

src/index.js

@@ -126,7 +126,7 @@ const customRule = {
 
         fragmentsHTML.push(...idOrAnchorNameHTMLFragments)
 
-        if (!fragmentsHTML.includes(url.hash.toLowerCase())) {
+        if (!fragmentsHTML.includes(url.hash)) {
           if (url.hash.startsWith("#L")) {
             const lineNumberFragmentString = getLineNumberStringFromFragment(
               url.hash,
@@ -157,6 +157,8 @@ const customRule = {
               })
               continue
             }
+
+            continue
           }
 
           onError({

src/utils.js

@@ -28,7 +28,7 @@ const convertHeadingToHTMLFragment = (inlineText) => {
           "",
         )
         .replace(/ /gu, "-"),
-    ).toLowerCase()
+    )
   )
 }