Added resolve() api entrypoint

Added resolve() api to compile a template and resolve it's dependency tree of template files used to generate that function:

```
jade.resolve('str',options) => 
{
  fn: [compiled function],
  dependencies: {
    [filepath]: {
      [include1path]: {},
      [include2path]: {
        [subinclude1path]: {}
      }
    }
  }
}
```

Also added the following tests:
```
  jade
    .resolve()
      ✓ should return the same function as compile as part of its output
      ✓ should list the filename of the template referenced by extends
      ✓ should list the filename of the template referenced by an include
      ✓ should list the dependencies of extends dependencies
      ✓ should list the dependencies of include dependencies
```