Allow one to style Log Record parameters separately

[bramus]

(Ref. Seldaek/monolog#212 (comment))

Right now entire records are styled. In some cases it might be feasible to separately style the level, level_name, channel, message, etc. parameters of a Log Record. Think of blinking text for example: blinking the message might not make it all that readable, yet blinking the level and level_name might be.

[aldenw]

@bramus I've made a pull request here #15 that I think provides this functionality in a nice way.

It leave the current behavior and so should not be breaking I believe, but allow you to set the colorization based on the $format parameter.