Change Fatal and add SetOutput

Fatal functions and methods now automatically print the stored events
after the fatal event. SetOutput added, it changes where events are
printed to (such as a file or stderr). Also, all setters now wait for
all pending events to be handled before changing the behavior of the
PriorityLog.
Document the log package.
Privatize claim and unclaim in log
Remove newline causing issues with Godoc
Merge pull request #59 from Jonbeek/Log

Documentation for the Log and more