feat: add more extensive named path matching

[richrdkng]

Instead of the possibility to only match letters, numbers, underscores, and dashes, e.g: (a-zA-Z0-9_-), add the feature for named paths to be able to contain the character /, e.g.:

// JSON config file
{
  // with @ prefix
  "@dist/umd": "./temp/dist/umd"

  // without @ prefix
  "dist/umd": "./temp/dist/umd"
}

const path = require('@nodewell/path')

// with @ prefix
path('@dist/umd')

// without @ prefix
path('dist/umd')