Strip control codes (including colors) from irc messages in debug output.

Should fix #350. Strip any control code from irc message to avoid messing terminal output.
I added StripControls() and StripControls_n() functions to the CString class to provide a generic way to strip control characters (can be reused for log `-sanitize` option).

Control codes are either color codes, or any character define in C0 and C1 sets:
https://en.wikipedia.org/wiki/C0_and_C1_control_codes