Change `render` method to private.
Remove unneeded test.

This tests the same as the `view` method.
Add `render` method to `Cuba::Render`.

Same as:

```
res.write(view(...))
```
Merge content into local variables.
Fix `template_path` for Windows users.
Update documentation of rendering templates.
Merge pull request #45 from frodsan/render

Change `Cuba::Render` to be similar to `Cuba::Mote`.