Bug fixes and improvements (#1348)

* Add "reference" for EN version. Bug fixes.

* Unify the figure reference as "the figure below" and "the figure above".
Bug fixes.

* Format the EN markdown files.

* Replace "" with <u></u> for EN version and bug fixes

* Fix biary_tree_dfs.png

* Fix biary_tree_dfs.png

* Fix zh-hant/biary_tree_dfs.png

* Fix heap_sort_step1.png

* Sync zh and zh-hant versions.

* Bug fixes

* Fix EN figures

* Bug fixes

* Fix the figure labels for EN version

en/docs/chapter_appendix/contribution.md

@@ -20,7 +20,7 @@ As shown in the figure below, there is an "edit icon" in the upper right corner
 
 ![Edit page button](contribution.assets/edit_markdown.png)
 
-Images cannot be directly modified and require the creation of a new [Issue](https://github.com/krahets/hello-algo/issues) or a comment to describe the problem. We will redraw and replace the images as soon as possible.
+Figures cannot be directly modified and require the creation of a new [Issue](https://github.com/krahets/hello-algo/issues) or a comment to describe the problem. We will redraw and replace the figures as soon as possible.
 
 ### Content creation
 

en/docs/chapter_appendix/installation.md

@@ -6,7 +6,7 @@ We recommend using the open-source, lightweight VS Code as your local Integrated
 
 ![Download VS Code from the official website](installation.assets/vscode_installation.png)
 
-VS Code has a powerful extension ecosystem, supporting the execution and debugging of most programming languages. For example, after installing the "Python Extension Pack," you can debug Python code. The installation steps are shown in the following figure.
+VS Code has a powerful extension ecosystem, supporting the execution and debugging of most programming languages. For example, after installing the "Python Extension Pack," you can debug Python code. The installation steps are shown in the figure below.
 
 ![Install VS Code Extension Pack](installation.assets/vscode_extension_installation.png)