Exclude partial templates from generation

The following partial templates should be excluded from generation:
- Templates with `.part` extension
- Folders in `templates/partials`

Both of the above should be configurable. Maybe something like this in `complexity.yml` would exclude files with extension `.blah` and directories named `dont-generate-me/`:

```
excludes:
- dont-generate-me/
- .blah
```

From @friedcell on Twitter: "my previous solution was to have filename.html.part, but am open to either folder or name filter. needs to be configurable though"

@friedcell any other requirements or things I should know? Other ideas about this? Feel free to file other issues with anything that's annoying or could be better, btw.

I'll try to get this in over the next day, but in the meantime a workaround is to use complexity 0.8.0.