Remove API uses of get/setFeature

[joeha480]

The get/setFeature methods are overused (in fact, they are relied on for normal operation, most notably for getting/setting a Table), this is confusing for new users of the API. The Embosser interface implies that some features can be set (via various "supports"-methods), but the relationship between this interface and EmbosserFeatures is completely implicit.

The get/setFeature should remain, but only for non-API use, meaning features not defined by the API.

[joeha480]

Replaced by brailleapps/dotify.api#21