Symbols: Improve symbol transformations

+ normalize leading whitespace
+ convert image tags ![alt-text](link] to alt-text
+ remove footnotes

syntaxes/Symbol List - Heading.tmPreferences

@@ -1,32 +1,32 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <plist version="1.0">
 <dict>
 	<key>scope</key>
-	<string>text.html.markdown markup.heading</string>
+	<string>text.html.markdown markup.heading - meta.whitespace.newline</string>
 	<key>settings</key>
 	<dict>
 		<key>showInSymbolList</key>
 		<integer>1</integer>
 		<key>symbolTransformation</key>
 		<string>
-			s/\[([^]]+)\]\([^)]+\)/$1/g;
-			s/\[([^]]+)\]\[[^]]+\]/$1/g;
-			s/\[([^]]+)\]/$1/g;
-			s/\s*#+\s*$//g;
-			s/^\s*#(#*)\s*/$1/g;
-			s/^#{5}/          /g;
-			s/^#{4}/        /g;
-			s/^#{3}/      /g;
-			s/^#{2}/    /g;
-			s/^#{1}/  /g;
-			s/^(-+)\s*$/       $1/
+			s/\!?\[([^]]+)\]\([^)]*\)/$1/g; 	# strip image or link urls
+			s/\[([^]]+)\]\[[^]]*\]/$1/g; 		# strip reference urls
+			s/\[\^[^]]+\]//g; 					# strip footnotes
+			s/^\s*//g;							# strip leading whitespace
+			s/\s*#+\s*\z//g;					# strip trailing hashes
+			s/^#{6}/          /g;				# indent atx heading 6
+			s/^#{5}/        /g;					# indent atx heading
+			s/^#{4}/      /g;					# indent atx heading
+			s/^#{3}/    /g;						# indent atx heading
+			s/^#{2}/  /g;						# indent atx heading
+			s/^#{1}//g;							# indent atx heading
 		</string>
 		<key>showInIndexedSymbolList</key>
 		<integer>1</integer>
 		<key>symbolIndexTransformation</key>
 		<string>
-			s/\s*#+\s*$//g;
+			s/^\s*//g;							# strip leading whitespace
+			s/\s*#+\s*\z//g;					# strip trailing hashes
 		</string>
 	</dict>
 </dict>