Clarify meaning filename that it also may contain path.

[monty241]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[ashovlin]

Could you also update the equivalent string on the library-specific configs?

For example, here for Log4net:

aws-logging-dotnet/src/AWS.Logger.Log4net/AWSAppender.cs

Lines 231 to 237 in 1db97e6

	/// <summary>
	/// Gets and sets the LibraryLogFileName property. This is the name of the file into which errors from the AWS.Logger.Core library will be written into.
	/// <para>
	/// The default is going to "aws-logger-errors.txt".
	/// </para>
	/// </summary>
	public string LibraryLogFileName