Faas Flow Versions Save

1. SDK Update, allow to fetch API State
2. Welcome message on template

Changes:

1. Ability to Pause/Resume a workflow. Use query to the flow function pause-flow={req_id} or resume-flow={req_id}
2. Ability to Stop a workflow. Use query to the flow function stop-flow={req_id}
3. In Memory StateStore Support (for Async and DAG one need to use external StateStore)
4. Ability to pass external requestId (one can pass an requestID with X-Faas-Flow-Reqid

An adaptation of of-watchdog.
As per openfaas in future all of the templates going to use the of-watchdog

This PR migrates from go template based on legacy watchdog to go-http-template based on of-watchdog. Along with that comes the below changes

• Faasflow library now completely stateless
• Faasflow puts unique request id in response, as X-Faas-Flow-Reqid Fixes #56
• Flow execution is much faster
• Fix issue with dynamic branch execution Fixes: #62
• Fine tuned API, much easier to chain operations
• Updated README

This release add the below major changes:

1. Add option to modify Request before its executed for function and callback
2. Allow to query DAG definition and removes DOT generation from flow
3. Fix issues with Dynamic Branch executions
4. Changes StateStore interface to more granular, allowing more operation to be permitted on top
5. Options are separated into more meaning full Groups

This faas-flow version is tested and released for the below features:

DAG Vertex with Subdag Nestes SUBDAG Execution Only (Non Data) Edge Multiple End Node support - Automatically add a reference node with end marker as:

end-<dagId>

Fix issue with tracing with duplicate ID vertex node

Supports:

Consul State Store v0.1.0
Minio Data Store v0.1.0

And Openfaas version

This faas-flow version is tested and released for the below features:

Sync Chain Async Chain Async DAG

The compatible StateStores are:

Consul State Store v0.1.0

The compatible DataStores are:

Minio Datta Store v0.1.0