v1.7

1. A new APECSS structure, APECSS_Interaction, to gather data needed for the computations of bubble-bubble interactions in multi-bubble systems. This includes a new file interactions.c in the source folder to compute interactions between bubbles considering incompressible interactions (frequently used in the literature) and a new model based on the quasi-acoustic assumption.
2. An update to the binaryinteraction test case, which now incorporates the newly developed structure and function to compute the incompressible interactions between the two bubbles.
3. A new test case, cavitationonset, based on Ida, M. (2009). Multibubble cavitation inception. Physics of Fluids, 21(11), 113302..
4. A new test case, sphericalclustertensionwave, of a monodisperse spherical shape cluster of 250 microbubbles. This includes also an example of how such multi-bubble simulations can be parallelized in a simple manner using MPI.
5. Updates to the documentation.