Added atomic file generator prototype
Some small style tweaks in the code and docs
Added test for atomic file generator
Added test for no pre-commit file error of atomic file generator
Refactored to Path::Class::tempdir
Tempdir of atomic file generator step is now tied to role lifetime

This may help when eager cleanup of large files is required because of space
constraints, but will hurt with over-eager cleanup when not required, because
later steps must wait for a cleanup they do not need. Maybe make this
configurable by consuming step in the future.
Fixed bug with temp dir lifetime
Added test for correct cleanup of atomic file generator temp dir
Rename test file to better match other names
Small style tweak in atomic role
Tidy test code
Merge pull request #11 from maxmind/eilara/atomic-file-generator

Added atomic file generator prototype