Make some "science use case" tests for the analysis tools

[eteq]

Right now some of the unit tests do things that aren't always that meaningful scientifically, like measuring the centroid of multiple lines or the like. That is often fine/good for unit tests, but we should make an effort to include some "is the science right" tests. In particular I'm thinking of:

• Build a fake spectrum known line properties and add noise
• Try the continuum subtraction algorithms
• Measure properties like EQW, flux, FWHM, etc
• Compare to the expected results for those given the noiseless line properties. These can't be exact checks for equality because of the noise, but something that's a "good enough" (e.g., is the centroid right to within a pixel or two).

(Note: some of the tests I'm referencing are in in-process PRs, so right now this is more of a "do it later" issue. Should become more relevant once those PRs are merged, though.)

[eteq]

(Btw, this might be a good thing for someone who's a bit less involved in the development/engineering but understands the science context!)