Ebs-snapper

- Be sure we only touch retention when touching functions (27)

- Ensure our log groups have default retention settings (25)
- Documentation and metadata updates (24)

- Add option to ignore retention settings, when necessary (14)
- Test parse configs before saving (18)
- Add support for ignoring certain volumes (16)

- Freshen dependencies. No functional changes.

- Bump to release latest HEAD as 0.4.1, no changes from v0.4.0.

Much of this work is related to 5.

- Switch to threading from multiprocess
- Pre-create API data in bulk
- Cut away the 'every DeleteOn tag' strategy
- Randomize order of snapshot and cleanup
- Make CLI perform full snapshot or cleanup
- Log when a snapshot is completed, improve duration check
- Reduce tag lookup calls, clean up, add more sleep