Implement multiline and hints support

Implement multiline and hints support

multiline and hints support now matches antirez/master

Additionally:
- Use an expanding stringbuf to simplify management of the current line
- Now there is no maximum line length
- All output is buffered in refreshLine() and output at once to improve
  performance
- Remove insert/delete char optimisation since it fails with control chars
  and wide characters
- General code cleanup
- Support CRNL in addition to NL for EOL
- don't allow ^V to insert a null char
- Coloured prompts using ANSI escape sequences are now supported on both windows
  and non-windows
- Example app now supports a custom prompt

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