Add support to specific route in express

[jacsamg]

Hi! 🙂

I added a new option that allows to use the integrated middleware through a specific route in express.

In the issue #15 had proposed a solution, but after reviewing the code calmly, I realized that the problem was only in the method that returns the versioned path: getVersionedPath.

It happens because when adding a route for the middleware, the method getVersionedPath has no knowledge of it, and continues to return the direct path.

With the new option it is possible to specify that the middleware will pass through a route.

The new option is used in the getVersionedPath method. In this way, it returns the path correctly even when there is a specific route for the middleware.

Example of use:

var path = require('path');
var options = { mwRoute: '/assets' }
var staticify = require('staticify')(path.join(__dirname, '/public'), options);

app.use('/assets', staticify.middleware);
app.locals.assets = staticify.getVersionedPath;

I await your comments. 👍

Fixes #15

[XhmikosR]

@tojacob: can you add tests?

[jacsamg]

@XhmikosR:
Currently I do not have much experience with the test libraries.
But I added the test for the new mwRoute option. I think it covers what is necessary in a test.

[rakeshpai]

LGTM! Thanks for the PR, @tojacob.

I know this is bikeshedding, but is mwRoute the best name? Could we call it prefix or 'pathPrefix' or something along those lines? Open to suggestions.

[XhmikosR]

Note that this should be squashed into one commit when merging.

[jacsamg]

@rakeshpai: It's true, I have serious problems with names.
It seems to me that pathPrefix looks great, it is even self-explanatory, because it is used with the getVersionedPath method. I'll change it so that it's ready.

@XhmikosR: Okay!