syntax: markdown: new file -- coloring rules for Markdown files

First-draft-by: Ryan Westlund <rlwestlund@gmail.com>

syntax/Makefile.am

@@ -21,6 +21,7 @@ pkgdata_DATA =	asm.nanorc \
 		lua.nanorc \
 		makefile.nanorc \
 		man.nanorc \
+		markdown.nanorc \
 		nanohelp.nanorc \
 		nanorc.nanorc \
 		nftables.nanorc \

syntax/markdown.nanorc

@@ -0,0 +1,34 @@
+## Syntax highlighting for Markdown files.
+
+syntax markdown "\.md$"
+comment "<!--|-->"
+
+# Quoted:
+color magenta "^[ 	]*>.*"
+
+# List-item markers:
+color brightmagenta "^(    |	)* ? ? ?(\*|\+|-|[1-9]+\.)( +|	)"
+
+# Emphasis and strong:
+color green "\*[^*]+\*|_[^_]+_"
+color brightgreen "\*\*[^*]+\*\*|__[^_]+__"
+
+# Strikethrough:
+color red "~~.+~~"
+
+# URLs and links:
+color brightblue "\[[^]]+\]\([^)]+\)"
+color brightmagenta "!?\[[^]]+\]"
+
+# Code, indented code, and fenced code:
+color brightcyan "`[^`]+`"
+color brightcyan start="^(    |	)+([^*+0-9> 	-]|[*+-]\S|[0-9][^.]).*" end="^$"
+color brightcyan start="```" end="```"
+
+# Headings and the underlining of headings:
+color brightyellow "^#.*"
+color brightyellow "^(=+|-+)$"
+
+# HTML tags and comments:
+color cyan "<[^>]+>"
+color cyan start="<!--" end="-->"