Add ExpressValidator class

[gustavohenke]

Description

This adds the ExpressValidator class, which can hold extension validators, sanitisers and default result formatters.

It can be used like this:

const { check, body, checkSchema, validationResult } = new ExpressValidator(
	// Custom validators
	{ isAllowedDomain: value => { ... } },
	// Custom sanitizers
	{ removeDomain: value => { ... } },
	// Options. Currently only errorFormatter
	{ errorFormatter: error => `Error of type ${error.type}` },
);

app.post('/new-user', [
	check('email')
		.trim()
		.isEmail()
		.isAllowedDomain()
		.removeDomain()
], (req, res) => {
	console.log(validationResult(req).array());
	// => 'Error of type field'
});

To-do list

• I have added tests for what I changed.

• This pull request is ready to merge.

[coveralls]

Coverage: ?%. Remained the same when pulling c250ff8 on v7-express-validator-instances into 92e0752 on v7-features.

[coveralls]

Coverage: 100.0%. Remained the same when pulling 020cd06 on v7-express-validator-instances into 92e0752 on v7-features.