Fix #265 - Add float-right and float-left responsive classes

Introduces the new semantics:

```
.float-left-xxsmall
.float-right-xxsmall
.float-left-xsmall
.float-right-xsmall
.float-left-small
.float-right-small
.float-left-medium-small
.float-right-medium-small
.float-left-medium
.float-right-medium
.float-left-medium-large
.float-right-medium-large
.float-left-large
.float-right-large
.float-left-above-xxsmall
.float-right-above-xxsmall
.float-left-above-xsmall
.float-right-above-xsmall
.float-left-above-small
.float-right-above-small
.float-left-above-medium-small
.float-right-above-medium-small
.float-left-above-medium
.float-right-above-medium
.float-left-above-medium-large
.float-right-above-medium-large
.float-left-above-large
.float-right-above-large
```

These behave similarly to the `hide-X` and `hide-above-X` classes. See #265 for more information.