Tasks as npm modules

[tiagofilipe12]

Tasks could be npm modules and then one could import them as such:

const { join } = require('bionode-watermill')
const samtools = require('watermill-samtools')

const  pipeline = join(stuff, stuff2, samtools)

[thejmazz]

Blocked by #75.

First step will be modules within this repo.

Also - we should probably spec out all the responsibilities of a task module by the time we make some of these published:

• how to do tests for it
• how to include example files
• how to include corresponding CWL (see #45)
• recommend to include examples that fail (e.g. common failures, index file not present)
• custom logic for that tool (e.g. watch stdout stream and fail task if certain pattern is found - useful for programs that fail but do not give 0 exit code)
• how the documentation/readme template should be (we want to be consistent across task modules)