notify formatter of different failure types
track failed notifications rather than examples

note I'm in half a mind to track these in the reporter instead, WDYT
@myron_marston?
extract failure message lines
extract backtrace handling
move specs for reading backtrace lines, this will need more refactoring me thinks
update yard
minitest assertion output changed, unsure why
use instance_doubles
changelog for #1510
Merge pull request #1510 from rspec/extract_formatter_backtrace_handling

Extract formatter backtrace handling