Create equivalents for `hb-view` and `hb-shape`

[asibahi]

Hello,

It might be useful as a tool to have binaries with direct access to the shaper's internals to prototype views and ideas. Creating a command line app that just takes the font and the text and gives output is trivial, but there are a lot of different options and knobs to tweak the output.

The question is, if rustybuzz were to add equivalents (say rb-shape and rb-view, is it important to follow the same options/interface as much as we can or should it do its own thing?

You can see the different options with $ hb-view --help-all

[RazrFalcon]

We already have hb-shape: cargo run --example shape
As for view: #70