Add regex search, search/replace, and buffer read-only mode functionality with help text

ROADMAP.md

@@ -1,10 +1,10 @@
 ROADMAP / TODO:
 
 - [x] Search + Replace
-- [ ] Regex search + replace
+- [x] Regex search + replace
 - [ ] The undo system should actually work
-- [ ] Able to mark buffers as read-only
-- [ ] Built-in help text
-- [ ] Shorten paths in the homedir with ~
-- [ ] When the filename is longer than the message window, scoot left to
-  to keep it in view
+- [x] Able to mark buffers as read-only
+- [x] Built-in help text
+- [x] Shorten paths in the homedir with ~
+- [x] When the filename is longer than the message window, scoot left to
+  keep it in view