[volume] Update create_snapshot docs
[volume] Added get_snapshot_details request
[volume] Added list_snapshots request
[volume] Added update_snapshot request
[volume] Added delete_snapshot request
[volume] fix list_snapshots
[volume][tests] add delete_snapshot_test & cassettes
[volume][tests] add update_snapshot_test & cassettes
[volume][tests] add list_snapshots_test & cassettes
[volume][tests] add get_snapshot_details_test & cassettes
Merge pull request #31 from stefanymarie/feature/AVIATORAPI-58

Feature/aviatorapi 58 (volume snapshot api)