Adding support for loading custom rulesets off the filesystem.

[erunion]

This adds support for being able to supply a custom ruleset on your filesystem to the lint command.

Examples!

$ cat standards.json 
{
  "require": "strict",
  "rules": []
}

$ ./node_modules/.bin/speccy lint --verbose --rules=./standards.json docs/3.4/openapi/api.yaml 
READ ./standards.json
READ /Users/ursenbachj/code/vimeo-api/design/node_modules/speccy/rules/strict.json
READ /Users/ursenbachj/code/vimeo-api/design/node_modules/speccy/rules/default.json
Found 18 rules in default: parameter-description,parameter-name-regex,operation-operationId,operation-summary-or-description,operation-tags,path-keys-no-trailing-slash,server-trailing-slash,openapi-tags,openapi-tags-alphabetical,reference-no-other-properties,pathItem-summary-or-description,example-value-or-externalValue,default-and-example-are-redundant,reference-components-regex,no-script-tags-in-markdown,info-contact,license-apimatic-bug,no-eval-in-descriptions
Found 5 rules in strict: contact-properties,license-url,server-not-example.com,tag-description,short-summary
Found 0 rules in ./standards.json: 
GET docs/3.4/openapi/api.yaml
Specification contains lint errors: 596

#/info/contact  R: contact-properties  D: contact object should have name, url and email
expected Object { url: 'https://developer.vimeo.com/help' } to have property name

More information: https://speccy.io/rules/#contact-properties

...

standards.json is loaded off my filesystem, which then requires the stock strict rule, which then also requires default.

Supplying a ruleset name, like strict, still works as well:

$ ./node_modules/.bin/speccy lint --verbose --rules=strict docs/3.4/openapi/api.yaml 
READ /Users/ursenbachj/code/vimeo-api/design/node_modules/speccy/rules/strict.json
READ /Users/ursenbachj/code/vimeo-api/design/node_modules/speccy/rules/default.json
Found 18 rules in default: parameter-description,parameter-name-regex,operation-operationId,operation-summary-or-description,operation-tags,path-keys-no-trailing-slash,server-trailing-slash,openapi-tags,openapi-tags-alphabetical,reference-no-other-properties,pathItem-summary-or-description,example-value-or-externalValue,default-and-example-are-redundant,reference-components-regex,no-script-tags-in-markdown,info-contact,license-apimatic-bug,no-eval-in-descriptions
Found 5 rules in strict: contact-properties,license-url,server-not-example.com,tag-description,short-summary
GET docs/3.4/openapi/api.yaml
Specification contains lint errors: 596

#/info/contact  R: contact-properties  D: contact object should have name, url and email
expected Object { url: 'https://developer.vimeo.com/help' } to have property name

More information: https://speccy.io/rules/#contact-properties

...

[coveralls]

Coverage decreased (-0.04%) to 87.824% when pulling 5cb7ce0 on erunion:local-custom-rulesets into 2008684 on wework:master.

[coveralls]

Coverage decreased (-0.04%) to 87.824% when pulling 5cb7ce0 on erunion:local-custom-rulesets into 2008684 on wework:master.

[coveralls]

Coverage decreased (-0.04%) to 87.824% when pulling 5cb7ce0 on erunion:local-custom-rulesets into 2008684 on wework:master.

[philsturgeon]

Thank you! I had this change in a random branch somewhere but it was wrapped up with other changes, and yours has a nicer test. Thanks for getting this done!