Add most of the remaining math filters

[teburd]

• times
• divided_by
• ceil
• floor
• round

[johannhof]

Hey, thanks for contributing! Your PR is looking good, just two minor things:

• you'll have to rebase on master, sorry for that :)
• I'd love if you could add assertions for the error returning paths as well, doesn't have to be fancy (e.g. call "ceil" with a string and check it returns an error)

Thank you!

[teburd]

I spent few thinking about a way to make a macro for testing error returns without adding a bunch of fluff, might take me awhile. This was rebased otherwise though with the success cases tested so far.

[johannhof]

Can't you just do

assert!(ceil(Bool(true), &[]).is_err());

? :)

[teburd]

Right, I was for whatever reason thinking testing the error type and string would also be good, but I guess just showing its an error scenario would be good enough

[johannhof]

Great job, thank you! 👍