v0.3.9

Trixi v0.3.9

Diff since v0.3.8

Closed issues:

• Weird results for timing of Euler+gravity (#418)

Merged pull requests:

• fix linear structure and convergence test (#417) (@ranocha)
• correct timings for Euler+gravity; fixes #418 (#420) (@ranocha)
• Add script for using PackageCompiler.jl (#422) (@sloede)