#130 add bootstrapper

**Update - I've tidied and fixed up docs and added minimal testing. I think this change is worth considering for inclusion.**
(was *Not a final PR. Just soliciting slightly early feedback on my attempt at #130.*)

I hacked this together last night. It's not very good, but it appears to function, and I thought I'd solicit early feedback so people can complain about the overall approach or something before I start polishing.
Problems I know about, but don't mind taking comments on.

1. no automated tests
1. the names are not fantastic (would love suggestions, if you got 'em)
1. we could maybe put the bootstrapper and put it in ServiceLocator instead of using the locator in ImportsModule. Of course, maybe YAGNI.

The overall approach is simpler than, for example, Nancy's. Mostly because I'm not sure we need the sophistication. Places where I intentionally deviated:

1. exposed all methods on the IBootstrapper interface. I think it's more straightforward for the overrider. Of course, overriding DefaultBootstrapper is still the preferred route
1. no intermediate configuration object or anything—we're getting what we want right from the bootstrapper

I'm happy to reconsider all points, of course.

@megakid, I figured you'd be interested in the implementation and also might enjoy early access, just to give things a spin. You can pull and build or get [a built version from my DropBox](https://www.dropbox.com/sh/yvrt1efvhh29g42/KrIUlm-9xy).

When I was noodling around, here's what I used to turn off the scanning:

```csharp
public class NonScanningBootstrapper : FakeItEasy.DefaultBootstrapper
{
    public override IEnumerable<string> GetAssemblyFilenamesToScanForExtensions()
    {
        return Enumerable.Empty<string>();
    }
}
```