add .ruby-version file

For rubyenv and chruby to pick up
add new empty backlog
add better test config

- expose mock method
- Turn config to be more informative when encountering errors
add shovel items into a backlog
use a user_story object for backlog item mock
add backlog title to the constructor
add backlog refinement: add pbi's to the backlog
add Epicable behaviour

- Epicable duck type found
- Epicable interface tests
- Backlog#epics collection
add ability to breakdown epics in backlog
move breaking down epic tests into unit tests
set a default epic value
raise error on breaking down non epics

Throwing an error meant that some acceptance tests were no longer
relevant.
extract double definitions into their own files
raise error if epic replacements not specified

when breaking down an epic
move breakdown validation into private method
extract breaking down epics into its own service
require lib files
shorten require statement for lib files
move epic behaviour out of backlog class

and into backlog refinement class
move backlog errors to backlog refinement class

As this is now the class that is using them for checking it's
behaviour