schema builder fluency (fixes #303)

[JoshMcCullough]

Breaking Changes

Schema.Builder needs to return the subclassed builder instance rather than Builder<S> in order to allow for fluency while building schemas. See related issue.

Note: I also renamed ConstSchema.ConstSchemaBuilder to just Builder to match the other builders for consistency. I can pull this change back out if you don't want it. Since this PR is already a breaking change, I figured it made sense.

[JoshMcCullough]

I'm trying to figure out how to instruct japicmp that it's okay that I renamed that class since this would be released as a new major...

[JoshMcCullough]

Okay, updated the japicmp config to allow these changes for a major bump.

[coveralls]

Coverage decreased (-0.02%) to 91.474% when pulling 17fc6f7 on JoshMcCullough:jsm/schema-builder-fluency into da6e9fd on everit-org:master.

[erosb]

Hello @JoshMcCullough , thank you for your work on this. I'm afraid we won't break backward-compatibility and increment the major version number for the purpose of this single fix (and other potential breaking changes are not under discussion right now).

[JoshMcCullough]

@erosb I understand the hesitance. And I can work with it using my own fork. I will just point out that creating a fluent schema as it is now is possible. But a general user would be confused if they tried it. I hope you'll bring this in at some point. Version numbers are just numbers, after all, and that's the point of semantic versioning. I would understand if you wanted to wait before doing so, but hope it's on your roadmap.

[erosb]

Yes, I thought about the same fix years ago. Thanks for the PR. Let's leave it open for now, and we will merge it when 2.0 is on the line.

[JoshMcCullough]

Opened new PR: #465