Dynamic redirections.

Fixes #108

The `redirects.json` file is renamed into `redirects.js`, and it is now a module which must export the array of redirections. Redirections can have dynamic parts, or be regular expressions. Self-explanatory example:

```
module.exports = [
{
  from: "/redirect1/{dynamic}/{route}",
  to: "/new/{route}/{dynamic}"
}, {
  from: /\/redirect2\/(\d+)-\d+-(\d+)-(\d+)/,
  to: "/new/{1}/{0}/{2}"
}];
```