Deprecated.the use of this interface must be replaced by the use of the
MonologFactory interface. This interface is kept for the backward
compatibility.
This field reference the level names by their integer value.
key = a java.lang.Integer which the value is the level
value = a String or an ArrayList of String.
this abstract class provides with the way to define a file real path with
the value of environment variables value.
to do that, the path in the the log properties file must include some variable
name those environment variable must be put in braket like ${MY_VARIABLE}