Add `scope` to CLI and tsconfig options; un-deprecate `TS_NODE_SCOPE`

[cspotcode]

Add --scope to the CLI and add scope as an option which can be specified in tsconfig.json
Un-deprecate TS_NODE_SCOPE
Update docs
Update ts-node --help output
Update: also added TS_NODE_SCOPE_DIR and --scope-dir / tsconfig scopeDir in #1367

• double-check my old issues about scope to ensure there are no reasons against adding it to tsconfig.json

Motivating use-case

Based on conversation starting here:
#693 (comment)

• The user has a monorepos, ./packages/a/node_modules/b symlinks to ./packages/b
• running tests and scripts in ./packages/a
• allowJS is enabled
• code in a imports b, which resolves to ./packages/b/dist/index.js
• The user does not want ts-node to compile anything in b; only in a
  • philosophically, each package in the monorepo is a separate entity with its own build scripts
  • One package should not make assumptions about its ability to transpile the source of another
• rootDir is ./packages/a/src but ts-node is running unit-tests in ./packages/a/unit-tests
  • This can be addressed by overriding rootDir for ts-node