The compiled "checker" should accept path & parent

[HCanber]

Previous functionality

In 0.3.0 - 0.6.10 the returned function from compile looked like this:

function(obj, _schema, pathStack)

0.3.0: https://github.com/icebob/fastest-validator/blob/v0.3.0/lib/validator.js#L128
0.6.10: https://github.com/icebob/fastest-validator/blob/v0.6.10/lib/validator.js#L169

_schema was never used but pathStack was, so it was possible to provide a custom path from code:

const v = new Validator()
const validate =  v.compile(schema)
const result = validate(myObject, null, 'custom.path')

The custom path was used in error messages and also become part of the path forwarded to custom validators, so they could use that info when validating.

Current functionality: Breaking change

In 0.6.11 this was changed to:

function(value)

This was breaking change and broke some of our tests, where we use fastest-validator to validate parts of the objects. Custom validators that relies on path in the same way as the example above are used. Currently we have locked to use version 0.6.10

Restored functionality

This PR brings back the 0.6.10 functionality, however; As a breaking change already was introduced in 0.6.11, instead of restoring 0.6.10 functionality as it was (with an unused _schema argument) the returned function now looks like this.

function(value, path, parent)

So it's still a breaking change to what 0.6.10 looked like, but at least it makes it possible, after changing calls from validate(myObject, null, 'custom.path') to validate(myObject, 'custom.path'), to provide custom paths.

Tests

Tests have been added that verifies

• that path, and when calling compile with schemas in an array: parent is used.
• that calling the returned checker, without path and parent, still works.

To be clear: This PR introduces no breaking changes to 0.6.12

[coveralls]

Coverage increased (+0.4%) to 100.0% when pulling 691887f on HCanber:compile-fix into d4efae5 on icebob:master.

[icebob]

Thank you!