Add Continuum removal of the spectra

[Bluejee]

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Is your feature request related to a problem? Please describe.
The spectra's of LIBS data that are available are not always ideal, the spectra might be having an underlaying continuum which causes the intensities of the peaks to shift upward. Although the qualitative aspects of the continuum wont be affected as much, removal of continuum will help in better assessment and quantitative analysis of the spectra.

Describe the solution you'd like
Add a function that can take in a spectra and return the continuum removed form for the spectra.