- and install it as a devDep

- doctoc is used in the README ToC and listed in comment, but wasn't
  a devDep or used in any internal scripts

- and use ensureDistFolder since that exists now
- and use async readJSON since most were converted before

- add types for all options and use those types throughout the
  build/watch code
- fix some incorrect types in a few places that became more obvious
  or errors once types were added
- fix default target from 'web' (not an option) to 'browser'

- extract createBuildConfigs into a separate file as it's fairly long
  and has some relatively complex code
  - and refactor it a bit to make it a bit easier to read as well as
    easier to type (and type cast)

Co-authored-by: Jared Palmer <jaredloganpalmer@gmail.com>

- similar to the ones that exist in react-app-rewired and customize-cra
  as, like CRA, changing TSDX internals is a fragile path

Specifically, rollup-plugin-node-resolve and rollup-plugin-commonjs.

- fs.outputFile will create any directories that don't already exist

- also remove extraneous ensureDistFolder w/ try-catch in build command

- not sure why this change was made in that PR as it was unrelated to
  the rest, but it broke some things related to Babel usage and maybe
  other things
  - e.g. babel macros were not included per #413
  - and it used `tslib` instead of adding babel helper functions

- add a comment of why it seems like the target is overriden to esnext
  - though I am not sure of the original reasoning, as it has existed
    since very early versions of TSDX, see #130 comments