Add Webster algorithm for sleep-wake scoring

[danielvartan]

Comments in English, Spanish, or Portuguese are welcome.
Comentarios en inglés, español o portugués son bienvenidos.
Comentários em inglês, espanhol ou português são bem-vindos.

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Instructions

• Create a branch called feature/webster.
• See all the references in the basic references section before starting the development.
• The function must take an object of class tsibble (mandatory).
• Add a vignette, with practical examples, explaining the features.
• All exported functions must be fully documented.
• All functions must be accompanied by unit tests (100% coverage).
• References in the documentation must be formatted in accordance with the APA (American Psychological Association) manual.
• When finished, create a PR to the main branch. Don't forget to mention this issue when creating your PR.

Materials

• Actigraphy log.
• Guidelines for Contributing.

Basic references

• Webster, J. B., Kripke, D. F., Messin, S., Mullaney, D. J., & Wyborney, G. (1982). An activity-based sleep monitor system for ambulatory use. Sleep, 5(4), 389-399. https://doi.org/10.1093/sleep/5.4.389

Other references

• American Psychological Association. (2020). Publication manual of the American Psychological Association (7th ed.).
  https://doi.org/10.1037/0000165-000