Touchdown

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- Fix as_seconds for tail command (regression introduced in 0.15.6)

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- AWS S3: Fix regression in syncing a local folder to S3.

- SSH: Fix regression shelling in to boxes with 'ssh'

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- AWS EBS: Fix racey volume attachment code.

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- Core: Ensure that an argument.Serializer or similar contributing to a
serialization is always considered present.

- AWS AutoScaling: Fix regression where tags aren't correctly set.

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- AWS LaunchConfiguration: Fix regression where json_user_data field stops
user_data field from working.

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- VPC: Support VPC Endpoints. These allow private network interfaces to access
S3 without needing NAT etc.

- KMS: Fix key deletion.

- Core: progressbar2 integration has been removed.

- Windows: Fix unix epoch handling in AWS CloudWatch log tailing.

- Core: Fix some issues around pending resources that could break very early on
for **fresh** deployments (from scratch).

- Config: Fix a case where a key is present but has no value breaking things.