Support logging of IRC colours

[Zarthus]

It would be nice to have a setting that ensures colours do not get removed in the logging.

Some usecases:

• Paste messages exactly as they were received
• Ban a specific annoying realname that has a weird and/or annoying colour combination that is no longer available in WHOWAS.
• Easier grepping when you know a message you're looking for has used colours.

[BlacklightShining]

Would this just cover colors? I'd like my logs to include all formatting—really the message as it was received, like @Zarthus said.

[Zarthus]

A good point - yes, the intention is to "log the message as it is", just in a weechat-readable logging method. (i.e. no raw irc message logging, but without weechat stripping things from the message either)

[flashcode]

I'll add an option to write log files with ANSI color codes, and then display of backlog will be in color by default if this option is enabled (#621).
If ANSI color codes are written, the log file can be read with less -R filename, and it will probably break scripts reading log files like grep.py. So they'll need an update to support ANSI color codes.

I'll add a modifier "color_encode_ansi", that converts WeeChat colors to ANSI colors (a similar modifier "color_decode_ansi" already exists to convert ANSI colors to WeeChat colors).