feat!: 致谢标题支持用const/heading/acknowledgements调整，同时英文模板默认值从单数改为复数

致谢有 -edge-/-edg-、-ment/-ments 四种写法。

Relates-to: #496

bithesis-doc.tex

@@ -1442,11 +1442,21 @@ \subsubsection{常量名称覆盖}
 \begin{bitsyntax}[emph={[1]degree,major}]
   info = {
     degree = (*(申请学位级别)|\marg{字符串}*),
-    major = (*(学科专业)|\marg{字符串}*),
+    major = (*专业 | 学科专业 | Degree | \marg{字符串}*),
   },
 \end{bitsyntax}
 
-  用于定义封面中个人信息条目的各个常量值。
+  用于定义封面中个人信息条目的各个常量值。默认按论文类型自动设置。
+\end{variable}
+
+\begin{variable}[added=2024-07-09]{const/heading/acknowledgements}
+\begin{bitsyntax}[emph={[1]acknowledgements}]
+  info = {
+    acknowledgements = (*致谢 | Acknowledgements | \marg{字符串}*),
+  },
+\end{bitsyntax}
+
+  用于定义一些固定章节的标题。默认按论文类型自动设置。
 \end{variable}
 
 \section{正文编写}

bithesis.dtx

@@ -493,7 +493,7 @@
     {conclusion} {结\label_space: 论} {Conclusions},
     % 附录部分的总标题
     {appendix} {附\label_space: 录} {Appendices},
-    {ack} {致\label_space: 谢} {Acknowledgement},
+    {ack} {致\label_space: 谢} {Acknowledgements},
     {figure} {插\label_space: 图} {Illustrations},
     {table} {表\label_space: 格} {Tables},
     % 附录下各部分编号的前缀
@@ -762,6 +762,7 @@
     autoref .meta:nn = { bithesis / const / autoref } { #1 },
     style .meta:nn = { bithesis / const / style } { #1 },
     info .meta:nn = { bithesis / const / info } { #1 },
+    heading .meta:nn = { bithesis / const / heading } { #1 },
   }
 \keys_define:nn { bithesis / const / autoref }
   {
@@ -814,6 +815,13 @@
       }
     },
   }
+\keys_define:nn { bithesis / const / heading }
+  {
+    acknowledgements .tl_set:N = \g_@@_const_heading_acknowledgements_tl,
+    acknowledgements .initial:n = {
+      \@@_get_const:N {ack}
+    },
+  }
 %    \end{macrocode}
 %
 % 定义 |bithesis/style| 键值对类。
@@ -3032,11 +3040,7 @@
         subsubsection/number = \arabic{section}. \arabic{subsection}. \arabic{subsubsection},
       }
 
-      \@@_if_thesis_english:TF {
-        \chapter{\c_@@_label_ack_en_tl}
-      } {
-        \chapter{\c_@@_label_ack_tl}
-      }
+      \chapter{\g_@@_const_heading_acknowledgements_tl}
       \@@_if_graduate:TF {\fangsong}{}
       #1
     \end{blindPeerReview}