Implement transform module

The transform method is a wrapper on top of “parse-traverse-generate” tool chain. Getting a regular expression string, and the nodes handler, transform should return a new (transformed) regular expression.

The issue depend on ~issue #5~.

An example of manual traversal, and code generation is shown in the Using traversal API section. A transform version of it should look like:

const regexpTree = require('regexp-tree');

const re = regexpTree.transform('/[a-z]{1,}/', {
  // Handle "Quantifier" node type,
  // transforming `{1,}` quantifier to `+`.
  onQuantifier(node) {
    // {1,} -> +
    if (
      node.type === 'Range' &&
      node.from === 1 &&
      !node.to
    ) {
      node.type = '+';
      delete node.from;
    }
  },
});

console.log(re); // '/[a-z]+/'

[mathiasbynens]

My vote goes to option 4.

[shvaikalesh]

What should be return value of transform?

1. Receives string, returns string. Receives RegExp, returns RegExp.

• It is not cool when function returns values of different types (hey, strpos).

1. Always return string.

• It is a bit awkward to make RegExp from string.

1. Always return RegExp.

• new RegExp may fail in some envs because of unsupported syntax.

1. Return some Result object with toString and toRegExp.

EDIT: added downside of 3.