Merge 'yaml/types' into 'yaml' & fiddle with 'yaml/util'

[eemeli]

Especially with the port to TypeScript, it makes less sense now to expose 'yaml/types' separately from 'yaml'. So let's not.

This is how you'll need to update your imports, if using:

-import { Alias, Merge, Pair, Scalar, YAMLMap, YAMLSeq } from 'yaml/types'
+import { Alias, Merge, Pair, Scalar, YAMLMap, YAMLSeq } from 'yaml'

-import { binaryOptions, boolOptions, intOptions, nullOptions, strOptions } from 'yaml/types'
+import { scalarOptions } from 'yaml'
+const boolOptions = scalarOptions.bool

A couple of the 'yaml/util' exports also make more sense on 'yaml':

-import { Type, YAMLError, YAMLParseError, YAMLWarning } from 'yaml/util'
+import { Type, YAMLError, YAMLParseError, YAMLWarning } from 'yaml'

While we're at this, let's also add a couple of things to 'yaml/util' that weren't exposed before:

import { debug, warn, foldFlowLines } from 'yaml/util'

And finally, let's clear up things from the repo root that aren't needed anymore, or that we can easily hide in a config/ directory. Leaving the Prettier & ESLint config there at least for now, because otherwise editors wouldn't find them automatically.

If you're using ES modules in Node.js < 14.10, this may change how you need to import 'yaml/util', as the automatic named exports weren't generated for CommonJS imports until then. My suspicion is that this would affect a vanishingly small number of users, but please do let me know if it's a problem:

// Both forms are fine in Node.js 14.10 & later, and for all bundlers
-import { stringifyNumber } from 'yaml/util'
+import Util from 'yaml/util'
+const { stringifyNumber } = Util