Allow writing config file in es6, coffee, typescript

[vdanchenkov]

My suggestion is to make use of https://github.com/js-cli/js-interpret like it's done in webpack. For example, in order to enable babel transpiling of the config, user will have to do following:

1. npm install babel-register
2. configure .babelrc
3. rename config to .markdown-doctest-setup.babel.js

I can work on it and provide PR if you are ok with this change.

For those who came here looking for a solution, quick fix is to follow steps from above by putting this to .markdown-doctest-setup.js:

  require('babel-register')
  module.exports = require('./.markdown-doctest-setup.babel.js') 

[Widdershin]

@vdanchenkov since this tool already bundles babel, I've been considering just compiling the config before running. This would save user configuration, as ES6 would just work, but this might complicate the approach for typescript/coffescript.

What do you think?

[vdanchenkov]

@Widdershin I can imagine only one reason to use something different from es5 for config file. You do it if your project is written in given dialect already. For this case we can assume that all the configuration is done project-wide.

Idea is to pick up configuration of the whole project by simple file extension change.

Actually, my project is written in es6 and it's the only concern for me, but it would be good if other dialects happen to work out of the box in described way.

For reference, that's how I use it https://github.com/vdanchenkov/mobile-coverage-russia/blob/master/.markdown-doctest-setup.babel.js