rc: Add support for Mercurial

The script only highlights comments in commit messages, but it's a basis
to improve upon if more features are needed in a later time.

rc/base/mercurial.kak

@@ -0,0 +1,26 @@
+# https://www.mercurial-scm.org/
+# ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+
+# Faces
+# ‾‾‾‾‾
+
+face MercurialCommitComment cyan
+
+# Detection
+# ‾‾‾‾‾‾‾‾‾
+
+hook global BufCreate .*hg-editor-\w+\.txt$ %{
+    set buffer filetype hg-commit
+}
+
+hook -group hg-commit-highlight global WinSetOption filetype=(?!hg-commit).* %{
+    remove-highlighter hg-commit-highlight
+}
+
+# Highlighters
+# ‾‾‾‾‾‾‾‾‾‾‾‾
+
+hook -group hg-commit-highlight global WinSetOption filetype=hg-commit %{
+    add-highlighter group hg-commit-highlight
+    add-highlighter -group hg-commit-highlight regex '^HG:[^\n]*' 0:MercurialCommitComment
+}