Add support for creating a new empty buffer (C-k i).

- Introduced `BufferNew` command to create and switch to a new unnamed buffer.
- Registered `BufferNew` in the command registry and updated keymap and help text.
- Implemented `cmd_buffer_new()` to handle buffer creation and switching logic.

HelpText.cc

@@ -31,6 +31,7 @@ HelpText::Text()
 		"  C-k c        Close current buffer\n"
 		"  C-k d        Kill to end of line\n"
 		"  C-k e        Open file (prompt)\n"
+		"  C-k i        New empty buffer\n"
 		"  C-k f        Flush kill ring\n"
 		"  C-k g        Jump to line\n"
 		"  C-k h        Show this help\n"