Big cleanups to linenoise

Big cleanups to linenoise

- Use a structure (current) to hold the state.
- Add fd_printf() to simplify output
- Add has_room(), insert_char(), remove_char(), fd_read()
- Use ctrl(X) instead of magic numbers
- Escape special chars in the history file
- Provide access to the history lines
- Completion support is optional

Signed-off-by: Steve Bennett <steveb@workware.net.au>