fix tsc output and published package structure

[kherock]

I saw #8 open and thought I could make an easy fix here. I've found it usually gets confusing when you want to transpile src -> lib yet want to reference values from package.json at the project root or have test files outside of the src root directory. The way I've seen it done is to

• use a separate tsconfig.build.json setting rootDir and include[] to src
• to import values from package.json, either turn off resolveJsonModule and use require, or leave it on and use fs.readFileSync if you need json module types in other places

Aside from that, I also noticed the use of .npmignore wasn't doing a great job—files like .vscode/*, fixtures/*, tsconfig.json, etc. were getting into the package tgz. I've removed it and added "files": ["lib"], this is safe because of how most npm clients include/ignore files by default.

New package tree after these changes:

.
├── bin
│   ├── spack.js
│   └── swc.js
├── lib
│   ├── spack
│   │   ├── extensions.js
│   │   ├── index.js
│   │   └── options.js
│   └── swc
│       ├── dir.js
│       ├── file.js
│       ├── index.js
│       ├── options.js
│       └── util.js
├── package.json
└── README.md

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[kdy1]

Thanks!!