v0.19.0 - much bigger and more powerful

Supports writing files > 5MB to Google Cloud Storage. Fixed a crash with minio. A couple other small fixes including some directory mtime changes, although more of the latter is probably needed soon.

Bumped version to 0.19.0 from 0.0.18 to be more consistent with catfs versioning.

Built with go 1.9.2

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