add new config cornerExternalLinkTarget for the corner link target

rm   CNAME

add CNAME

add repo test

back to the origin index.html

fix: the Git corner displayed bigger when the externalLinkTarget = ''

[update] a new independent config for corner link target attribute.

[update doc] add the `cornerExternalLinkTarget` config in the doc.

docs/configuration.md

@@ -397,7 +397,7 @@ window.$docsify = {
 - type: `String`
 - default: `_blank`
 
-Target to open external links. Default `'_blank'` (new window/tab)
+Target to open external links inside the markdown. Default `'_blank'` (new window/tab)
 
 ```js
 window.$docsify = {
@@ -405,6 +405,19 @@ window.$docsify = {
 };
 ```
 
+## cornerExternalLinkTarget
+
+- type:`String`
+- default:`_blank`
+
+Target to open external link at the top right corner. Default `'_blank'` (new window/tab)
+
+```js
+window.$docsify = {
+  cornerExternalLinkTarget: '_self' // default: '_blank'
+};
+```
+
 ## routerMode
 
 - type: `String`