Derivative/extrapolation enhancement

[yoelcortes]

Hi Caleb,

This pull request implements the same extrapolation behavior as in extrapolate_integral. Tests were added too. There is a minor change in plot_T_dependent_property to allow extrapolation during a the test_documentation_plots test (calculate_derivative allowed for extrapolation before, but does not anymore).

Thanks!

[CalebBell]

Really great work Yoel! I may change some of the internal details of plot_T_dependent_property still. Again, please let me know if you want this in a release. Sincerely, Caleb

[yoelcortes]

Thanks! I did notice the tests ran slower due to using T_dependent_property_derivative in the plot_T_dependent_property method. I made some changes to reduce function calls there. I'm not sure what internal changes you are planning for plot_T_dependent_property, but I hope this helps!

I also added the algebraic solution for the integral extrapolation with some tests.

I'll go ahead and complete the merge.

Thanks again!