Add support for enums w/o needing to manually specify variations

[shane-tw]

Fixes #89

It will only attempt to figure out the variations if type:"enum" is specified and len(enums) is 0.
i.e. if someone uses the {enum} comment, or, for some reason, {enum: }.

The only edge cases I can think of here are in our own code, where we sometimes might not want "all" or "" exposed as enum options in the API even though they technically exist. In which case we'd still need to manually specify all the fields like we were doing prior to now.

[coveralls]

Pull Request Test Coverage Report for Build 12270279849

Details

• 35 of 51 (68.63%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.6%) to 56.902%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
docparse/jsonschema.go	35	51	68.63%

Files with Coverage Reduction	New Missed Lines	%
docparse/jsonschema.go	1	54.09%

Totals
Change from base Build 10494982151:	0.6%
Covered Lines:	1113
Relevant Lines:	1956

---

💛 - Coveralls

[pawel-banach]

LGTM 👍

[rafaeljusto]

Nice work with this feature request 👏

[aodhom]

Nice one on helping open source 😆

[shane-tw]

Despite the tests passing, this isn't working. My assumption is it's because we don't have any tests covering field types defined in another package/file. Investigating.