Add ability to plugins to colorize keywords and/or patterns

[jumar]

Current behaviour

Lines are colored according to log level only. The whole line has the same color.

Feature request

Add an API to allow plugins to colorize part of a log line with a given color if it matches a pattern.

It can be very usefull when analysing log files to have custom colors applied to certain strings or patterns. It help to see quickly important events in the logs.