Divvy

Changed
- Safer use of `yaml`
- Reduced verbosity for clearer usage
- The CLI now uses `divvy write` and `divvy list` subcommands

Changed
- For environment variable population, use updated version of `attmap`

Added
- Implemented a `divvy` command-line interface
Changed
- reduced verbosity

Changed
- `divvy` looks for computing configuration file path in both `$DIVCFG` and `$PEPENV` environment variables and the former is given priority
- `ComputingConfiguration` class extends `AttMap` class, not `AttributeDict`