This module provide a simple interface to filter entries out
of an httpd logfile. The constructor can be passed regular
expressions to match against particular fields on the
logfile.  It does its filtering line by line, using a filter
method that takes a line of a logfile as input, and returns
true if it matches, and false if it doesn't.

There are two possible non-matching (false) conditions; one
is where the line is a valid httpd logfile entry, but just
doesn't happen to match the filter (where "" is returned).
The other is where it is an invalid entry according to the
format specified in the constructor.
