Implementing functionality to make images from different number of scatterings.
Added tests for retrieving images with specific number of scatterings
Improvements to documentation
Extended changes to get_sed, and factored out duplicate code
Updated changelog
Fixed bug in index calculation
Merge pull request #99 from astrofrog/n-scatterings

Implement the ability to make images with a specific number of scatterings
Fix logic for killing photons
Added PR number [ci skip]
Merge pull request #100 from astrofrog/fix-n-interaction-limit

Fix logic for killing photons
Added new `kill_on_scatter` option
Merge pull request #101 from astrofrog/kill-on-scatter

Added new `kill_on_scatter` option
Add additional slices to contain remaining flux, so that a sum over the cube will return the total flux.
Added regression test for flux conservation
Merge pull request #103 from astrofrog/preserve-total-flux-nscat

Add additional slices to contain remaining flux, so that a sum over the cube will return the total flux.
Make ``get_quantities`` work for input files
Fixed a bug which meant that BipolarCavity instances could not be subtracted from the ambient medium
Added changelog entry
Merge pull request #106 from astrofrog/fix-bipolar-cavity-ambient-medium

Fix bipolar cavity ambient medium
Added I/O file for voronoi (same as octree for now)