Leveled execution logs for Go

This is an efficient pure Go implementation of leveled logs in the
manner of the open source C++ package
http://code.google.com/p/google-glog

By binding methods to booleans it is possible to use the log package
without paying the expense of evaluating the arguments to the log.
Through the -vmodule flag, the package also provides fine-grained
control over logging at the file level.

This package contains library source intended for
building other packages which use import path with
github.com/golang/glog prefix.