Refactor Code

[jrgant]

curvesim.R has gotten pretty bloated with all the functions:

• [x] Move functions into a separate file
• [x] roxygenize and make analysis repo into an R package
• [x] Document functions

[jrgant]

Documented the first two functions.

• [x] Some functions that appear in the code files should be moved into R/ and documented appropriately.
• [x] Write and document a function that automatically matches an epiweek to its integer week
• [x] Refactor code so that all epiweek-to-integerweek mappings use the same function (some of the matches are done differently across external datasets)