Description
-----------

A set of classes that can be used to implement the Log interface.
It provides more flexibility than other loggers in that both 
the time and message format may be fully specified by the user. 
This flexibility is afforded by use of the strfmt library but
this comes at the expense of being more expensive than a statically
defined canned format. 

Classes
-------

GenLogger is a standard logger that takes a Writer as an input.
StderrLogger and StdoutLogger are trivial wrappers for this
that can be used for their respective output types. FileLogger
also uses GenLogger but has additional options to specify file
creation options.

PolyLogger also implements the Log interface, and is a container
for multiple other Log implementations. For instance, you can 
add a FileLogger, a StderrLogger, and perhaps a 3rd-party logger
to a PolyLogger, and then set PolyLogger as your main application
log handler. A single info!/warn!/etc. call will cause the given
message to be logged by each logger in whatever format you have
specified in each logger, and with whatever level filter is 
applied to each logger.

Future Options
--------------

1. String Formatting

The runtime-fmt may be easier to use and faster than strfmt
for message formatting, but currently relies on the nightly 
build of rust features. 

In the meantime, it might be nice to create a set of statically
defined formats that would be more efficient than using the 
dynamically constructed strfmt method.

2. Producer/Consumer Queue in PolyLogger

The current implementation formats and logs all messages
sequentially in the same thread as the application. Moving 
to another thread (timestamping upon entry to the queue) 
would decouple this.