Updates the yt imports from imods to modds.
Merge pull request #3 from Pshriwise/3.0_update_fng

Updates the yt imports from imods to modds.
Added stuff for generating poly collections of plane-volume intersections.
Altered get_vol_tris function so it returns an entire volume's triangles in the same numpy array.
First take on creating poly collections for volume intersections.
Updated the adj_tris to be a full stack so all intersected (and connected) triangles of a surface are found at the same time.
Cleaned up the vol_intersections file a bit.
Added a file for the final cut of the poly intersection process.
Included lines for retrieving the triangles of each surface
Added the surface_intersections and intersection functions.
Added more necessary functions for getting surface intersections. Started dictionary for surface intersections.
Corrections to the intersections dictionary implementation.
Updated how the file is loaded and mesh sets are retrieved.
Implmeneted a function to retrieve intersections for a given volume.
Added a function for stitching intersections.
Corrections to the stitch function.
Updated stitch function to use del list[index] when checking for already-complete loops in surface intersections.
Refactor of surfce_intersections function.
Added a fix for conincident intersections and updatd the plot to polycollections
Updated plot to polycollection by volume