v0.13.18

Trixi v0.13.18

Diff since v0.13.17

Merged pull requests:

• Refactor Tree constructors (#2661) (@DanielDoehring)
• Remove unused code: AbstractContainer (#2662) (@DanielDoehring)
• An optimized 3D kernel for non-conservative fluxes (#2663) (@MarcoArtiano)