Removed redundant functions, fixed .gitignore

[swilliamson7]

Moved the checkpointed time integration function to its own script, I can't really think of a better way without adding using Checkpointing to the main ShallowWaters.jl file

[swilliamson7]

The diffs on time_integration.jl look weird to me, but they're correct on my computer so who knows

[milankl]

Moved the checkpointed time integration function to its own script, I can't really think of a better way without adding using Checkpointing to the main ShallowWaters.jl file

We could make Checkpointing an extensions, see https://pkgdocs.julialang.org/v1/creating-packages/#Conditional-loading-of-code-in-packages-(Extensions)

Then some code is only loaded when the user says using Checkpointing, how does that sound?

[swilliamson7]

Sure! That should work. I can make that into a separate pull request, for now I just haven't included the checkpointed time integration