Simple slow-rotation neutron star structure solver

I’m releasing into the wild a simple code for computing neutron star structure in the slow-rotation expansion to first and second order. This code was originally from Nico Yunes, with a bunch of development by Kent Yagi. I rewrote huge chunks of it to give it a command line/config file interface, turned some magic numbers into configurable parameters, C++ified some important bits, etc. Kent gave me his blessing to release it into the wild. For IP reasons, I first had to remove the dependence on code from Numerical Recipes, which is why it looks like the commit history starts in Sept. 2017.

Of course there are already codes like RNS and LORENE, so who needs another NS code? This code is useful for two reasons:

1. There is a modular implementation of the piecewise-polytropic model from Read, Lackey, Owen, and Friedman (2009) [arXiv:0812.2163] along with their fits for named EOSs; and
2. The slow-rotation expansion allows to accurately extract the moment of inertia and quadrupole moment.

Feel free to improve the code in any way you see fit and send me a pull request, or open a new issue, anything you want under the MIT license.