Develop an R package to link to TAF API

[colinpmillar]

Summary

write an R package that allows the user to query, post and update TAF assessments

Tasks required

• [x] develop token system for package
• [x] write functions in consistent style
• [ ] documentation and example
• [ ] release on CRAN

Links to other issues?

requires: Restructure TAF API using GitHub as inspiration #209