Octave pkg and Texinfo/QHelp support

[apjanke]

This thing needs to be installable as an Octave pkg package. Needs:

• Installability from a release URL
• Qt QHelp documentation support so doc <whatever> works

Use octave-chrono as a model for this. Except, now that this has a class with a bunch of methods, would be nice to add support for multi-part Texinfo documentation where each Texinfo fragment is positioned in the source code next to the method it's documenting, instead of requiring it all to be in a single block at the top of the classdef file.

Supporting multiple Texinfo blocks has some complications: helptext blocks attached to methods are logically associated with the methods, and they can be reordered based on class structure by the helptext interpreter. Texinfo is a linear document, and simply concatenating multiple Texinfo blocks found within the source code would tie the document structure to the source code ordering. Sigh.

Doing this will require additional build/release steps. Oh well; it's necessary.

[apjanke]

Okay, I added support for multi-block Texinfo doco here and in octave-chrono, and it's working out fine. Also added support for classes and namespaces in it.

You can install from master using the github archive URL, and that's in the README. So I think this is done.