Use libtool, fix Mac library issues

[ryandesign]

Hi, I'm the maintainer of stk in MacPorts. I've been meaning for years to report to you that there are several issues with the way your library is being created: it doesn't have an install_name set; it doesn't have versioning information set; its filename is unusual; your library versioning scheme may be incorrect or nonexistent. When I updated MacPorts stk to 4.5.0 I added patches to fix it well enough for our use, but your code has changed in the meantime.

It looks like @rdpoor has beaten me to it and reported some of this in #28 and #40 but no solutions seem to have been committed yet and those issues were closed.

The problems seem to stem from the fact that you generate shared libraries manually. Generating shared libraries accurately is apparently a complex topic. I could tell you all about how to make shared libraries on the Mac, but I have only a theoretical understanding of them on other systems. I could try to update my patches and submit PRs to you, but I'm not confident that I would make the best choices for everyone.

If you used libtool to generate the shared libraries, it would know the right thing to do on every operating system. Is there a reason why you don't use it here?

[garyscavone]

Honestly, I don't understand all the naming issues and the proper way to deal with them (my main interest in STK is the functionality of the code itself, not the packaging). If someone wants to submit a PR that addresses the issue, we can consider it.