[WIP] Added some math functions and helpers

[briederer]

Switched the order of upper and lower error for datapoints because it seems more reasonable to use it in this order (lower,upper).

Added some default constructors and type-specific ones which are needed when calling some functions with DataPoint types as an argument.

Need an opinion by @fzierler on how we treat the systematic uncertainties for things like relative error and region of datapoints.

[github-actions[bot]]

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[fzierler]

Need an opinion by @fzierler on how we treat the systematic uncertainties for things like relative error and region of datapoints.

I don't understand what you mean by that.

[briederer]

Need an opinion by @fzierler on how we treat the systematic uncertainties for things like relative error and region of datapoints.

I don't understand what you mean by that.

I mean if we want to have something like relerror(D::DataPoint) how is the correct way to handle systematic uncertainties? Should we then have one tuple with (stat_err .+ sys_err)./val or return two tuples for the errors independently?

I am also not sure if we even should keep the systematic error after all.

[fzierler]

I am also not sure if we even should keep the systematic error after all.

I agree. Let's get rid of them for now

[briederer]

Moved to #25