Update build and packaging scripts (#872)

- Add compile:release npm script to build the package without source
  maps. Decreases unpacked size from ~350KB to ~250KB.
- Remove :windows variants of npm scripts
  - Add rimraf to handle cross-platform dir removal
  - Set "ts-node": { "files": true } in tsconfig.json so that it's not
    necessary to set env var TS_NODE_FILES
- Remove unused assets/README.md (it does not appear to have been used
  for many years according to npmjs.com)
- Use includes "files": [...] property in package.json to indicate dist/
  should be included in the built npm package rather than maintaining a
  list of everything that should be excluded in .npmignore (which has
  been deleted)
- Incorporate above mentioned updates into build.sh

build.sh

@@ -1,16 +1,11 @@
 #!/bin/bash
 
 set -e
-trap 'mv _README.md README.md' EXIT
-
-mv README.md _README.md
-
-cp assets/README.md README.md
 
 rm -rf node_modules
 npm ci
 
-npm run compile
+npm run compile:release
 npm t
 
 echo 'publishing...'