* Add deprecation errors when attempting to set dateFormats of fileFormats that
break the possibility of rotating easily in RotatingFileHandler. Version 2.x
of Monolog will throw `\InvalidArgumentException`s in these cases.
- Require the dateFormat to be one of three presets ('Y-m-d', 'Y-m' or 'Y') to
ensure that dates can be sorted lexographically
- Require the filenameFormat to contain the (sub)string `{date}` so we will
actually create new files instead of the same file over and over again.
