Release v0.19.0

• Firecracker v0.19 API: Vsock API call: PUT /vsocks/{id} changed to PUT /vsock and no longer
  appear to support multiple vsock devices. Any subsequent calls to this API
  endpoint will override the previous vsock device configuration.
• Firecracker v0.19 API: Removed 'Halting' and 'Halted' instance states.
• Fixes a bug where fifos were not working properly with jailer enabled (#96)
• Fixes bug where context was not being used at all during startVM (#86)
• Updates the jailer's socket path to point to the unix socket in the jailer's workspace (#86)
• Fixes bug where default socketpath would always be used when not using jailer (#84).
• Update for compatibility with Firecracker 0.17.x
• Changes JailerCfg to be a pointer and removes EnableJailer for ease of use (#110).