Add naive import syntax support

[ctavan]

Given running esmodules in a node vm to truly evaluate code snippets as
esmodules is still experimental and pretty low level
(https://nodejs.org/docs/latest-v12.x/api/vm.html#vm_class_vm_module)
this hack might work in many cases already.

Demo:

console.log(
`
import { v1 as uuidv1 } from 'uuid';
import { v1 } from 'uuid';
import uuid from 'uuid';
import {
  v1 as uuidv1
} from 'uuid';
`
.replace(
  /import\s*\{\s*([^\s]+)\s+as\s+([^\s]+)\s*\}\s*from\s*['"]([^']+)['"]/g,
  'const { $1: $2 } = require("$3")',
)
.replace(
  /import\s*\{\s*([^\s]+)\s*\}\s*from\s*['"]([^']+)['"]/g,
  'const { $1 } = require("$2")',
)
.replace(
  /import\s([^\s]+)\sfrom\s*['"]([^']+)['"]/g,
  'const $1 = require("$2")',
)
);

Output:

const { v1: uuidv1 } = require("uuid");
const { v1 } = require("uuid");
const uuid = require("uuid");
const { v1: uuidv1 } = require("uuid");

[broofa]

Woot!

[ctavan]

BTW I also tried to get runmd to work in two different wais:

1. With true esmodule support / https://nodejs.org/docs/latest-v12.x/api/vm.html#vm_class_vm_module but I just couldn't wrap my head around it. Also it still feels very bleeding edge.
2. By bable-ing the source. That however didn't work well because you always have to bable full files in order to transform import statements… Since runmd executes code block-by-block that didn't work well.

After 3h I gave up and decided to go with this hacky workaround for now.