Serve roboto and roboto-mono locally (#57)

* Serve `roboto` and `roboto-mono` locally

* Include bold and italic variants for `roboto`

* Include bold variant for `roboto-mono`

* Include italic variant for `roboto-mono` (and unify directory structure)

`roboto` and `roboto-mono` now include the same set of fonts so this
commit also unifies the directory structure so it's consistent between
the two fonts, i.e.

```
├── roboto
│  ├── LICENSE.txt
│  ├── roboto-bold.woff2
│  ├── roboto-italic.woff2
│  └── roboto.woff2
└── roboto-mono
   ├── LICENSE.txt
   ├── roboto-mono-bold.woff2
   ├── roboto-mono-italic.woff2
   └── roboto-mono.woff2
```

Author: noxpardalis