add Burgers solver

[zingale]

Both viscous and inviscid

[zhichen3]

If nobody is working on this, I think I can start with this to help me get familiar with the code.

[zingale]

awesome!

[zingale]

this was done in #144

[zhichen3]

Oh, I thought we also want a viscous version as well.

[zingale]

ah indeed!

[zhichen3]

Viscous burgers solver was added in #171