added a new item content type: markdown

- emacs editor has an option to select markdown, now it has two planes: one for content editing and the other to show preview
- CodeMirror editor updated to 5.64.0
- to convert markdown to html we use showdown https://github.com/showdownjs/showdown (conversion is done on the client side)

winixd/models/itemcontent.h

@@ -94,6 +94,7 @@ public:
 		ct_html,
 		ct_bbcode,
 		ct_other,			// no auto-formatting is applied
+		ct_markdown,
 	};
 
 
@@ -278,6 +279,8 @@ public:
 	static void print_content(HtmlTextStream & out, const pt::WTextStream & content, ItemContent::ContentType content_type, bool is_html_filter_on);
 	static void print_content(HtmlTextStream & out, const std::wstring & content, ItemContent::ContentType content_type, bool is_html_filter_on);
 
+	void print_content(HtmlTextStream & str);
+
 	bool CanContentBeHtmlFiltered();
 
 	bool has_read_access(const User * current_user) const;
@@ -304,6 +307,9 @@ public:
 	bool is_link_to() const;
 	bool is_link_redirect() const;
 
+	static ContentType get_content_type_from_str(const wchar_t * str);
+	static ContentType get_content_type_from_str(const std::wstring & str);
+
 protected:
 
 	bool do_migration_to_1();