zFactor.DL 0.1.0

• replace sk_tidy.rda with a combined table of low and high pressure.
• make set column in both tables numeric.
• add column range to both tables indicating if lo or hi.
• create dataset sk_tidy_lp.rda for low pressure
• create dataset sk_tidy_hp.rda for high pressure
• read high pressure (Ppr) data points for z. use same HP notebook for low pressure. now we have two .Rda datasets in data.
• add extra notebook to read high pressure (Ppr) data points for z.
• added github logo to website
• Added pkgdown website to repo.
• sending website in docs folder to gh-pages.
• Added a NEWS.md file to track changes to the package.