marianschmidt/msSPChelpR: msSPChelpR 0.8.6

This is the first CRAN release for the msSPChelpR package.

• new sample data set for standard populations -> data("standard_population")
• new sample data set for us population -> data("population_us") (Closes #58)

• sir_byfutime(): change output of integer columns to numeric to fix bug in summarize_sir_results() (Closes #59)

• add examples to function documentation (Closes #56)
• remove "R" from package title (Closes #57)
• update package description (Closes #54)
• update introduction vignette vignette("introduction")