Tidal deformation

[matthiasfabry]

Following on #637, this (rather large) overhaul of hydro_rotation.f90 includes support for computing the stellar structure corrections of tidally distorted stars. This is especially useful when modeling contact binaries.

The setup is as follows:

I used procedure hooks (akin to binary_other_torque for tidal J_dot calculations) to communicate the binary calculated fp, ft, and i_rot values for the stellar layers.
Then these values are "blended" with the single-rotating-star corrections according to the synchronicity of the component to the orbit. I implemented a user hook binary_other_tidal_deformation_switch_function if one does not agree with this treatment.

The user can still use the other_fp_ft and other_i_rot hooks to bypass all default calculations (and blending).

[warrickball]

Not a blocker for me but would it be possible to use this in the test suite somewhere, be that in a new test or tweaking an existing one?

[Debraheem]

Certainly this needs a test_suite. I would love to test it out as well.

[matthiasfabry]

As a first test, double_bh contains a contact phase, plus it has strong tides, so this is a natural environment for the tidal deformation corrections. I incorporated a pgbinary window for good measure.