Generating code documentation for the public ALP/GraphBLAS API

[anyzelman]

The current make docs targets ALP/GraphBLAS developers, and accordingly generates too much information for ALP/GraphBLAS users.

As a bonus, the HTML documentations could be hosted on algebraic-programming.github.io

[anyzelman]

Associated merge request has gone into develop. Regular release cycle will make sure the public API docs are generated OK and will refresh the online version.