build command mvp

[jasonkuhrt]

Needs #10

Problem

Users must apply a specific combination of tools and configurations thereof to successfully build their app "the nexus way".

For example:

• Have the right two env vars in place
• Use ts-node
• Pass ts-node the right flags (--transpile-only)
• Ex: user not realizing they need special env var to trigger typegen on heroku deploy

Spec

At a high level:

• Run Nexus typegen
• Then run a real TS build

In Detail

• Assume that entrypoint is src/server.ts

• Set environment variable PUMPKINS_TYPEGEN='true'

• there should be an entrypoint flag for running typegen

• if user provides nexus entrypoint config in package json and user does not pass entrypoint cli flag then use the package json variant

• Use the Compiler API to find the user's tsconfig.json and honour it

• peer dep on typescript, using a range as wide as possible

We may want to use https://github.com/davidtheclark/cosmiconfig

• if no json config is found and no cli flag is passed then fallback to the following lookups:

src/schema/index.ts
src/schema.ts
src/server.ts
src/main.ts
src/index.ts
schema/index.ts
schema.ts
server.ts
main.ts
index.ts
ERROR (please pass entrypoint)

Some original build design started in #272 (comment) and original cli work began in #275.