#40 configurable formatter for method arguments

[Jason Trump]

as discussed in this forum thread:

https://sourceforge.net/projects/beet/forums/forum/939715/topic/3468295

anything other than a java primitive type gets logged as {object} in method events. This is an obvious limitation, and there's not a good way for end-users to extend this behavior.

as discussed on the forum, it would be nice to provide something like an 'ArgumentFormatter' interface that can be extended by applications. we need to be careful to prevent string formatting from generating events, or taking too much time from the application.