* 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
* fix(codes/cpp): Memory leak fix: the space was not freed when pop removed the element.
* fix(codes/cpp): Fix access error when printArray(arr, 0)
* Update PrintUtil.hpp
* fix(codes/c): Fix some errors of cmake build
* feat(codes/c): Add hashing_search.c
* styles(codes/c): Modify function description
* styles(codes/c): Modify binary_search.c code style
* fix(codes/c): Fix the problem in binary_tree_bfs.c and the problem that the memory is not released.
* feat: Add preorder_traversal_i_compact.c
* feat(codes/c): Add head_sort.c
* feat(codes/c): Add bucket_sort.c
* feat(codes/c): Add binary_search_edge.c
* fix(codes/c): Add programs that are not managed by cmake (c code)
* feat(codes/c): Add selection_sort.c
* style(codes/c): Change swap in selection_sort.c to `selectionSort`
* styles(codes/c): Change style.
* fix(codes/c): Fix some formatting errors and temporarily remove backtracking chapters
* fix(codes/c): Fix space_complexity.c build error.
* feat(codes/c): Add array_binary_tree.c
* feat(code/c): Update push_back and pop_back in vector.h
* styles(codes/c): Adjust format.
* style: Remove unnecessary print.
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Co-authored-by: Yudong Jin <krahets@163.com>
