Version 0.2.0
 - Trap exceptions in debugf and tracef
 - Trapped exceptions in debug* trace* are now reported using ->warn
 - New filter level 'all' suppresses all messages
 - Filter levels are now stored in symbolic form, for useful inspection by
   end-users
 - Invalid filter levels from environment variables no longer throw exceptions
   (only warn).  Filters from constructor args still do.
 - Fixed bug in filter="level+N" notation
 - Print helpful TAP comment about available environment variables on startup
 - Support for all log levels, rather than artifical cap at critical/fatal
 - Better support for subclassing (BEGIN block broken into reusable functions)
 - Publish default_dumper method instead of the _default_dumper function

Version 0.1.0
 - Basic support for all logging methods, prefixing all output with
   the canonical name of the log level other than 'info', and writing
   each line with a comment prefix.
 - Warning and higher go to STDERR like Test::More::diag, and Notice
   and below go to STDOUT like Test::More::note
 - Default filter is debug and below.
 - Support for custom dumpers, used for non-scalars passed to 'debug'
   or 'trace' or any of the formatting '*f()' functions.