import functions from epibuffet

[zkamvar]

This ports a lot of the functionality over to https://github.com/R4EPI/epibuffet and removes some tests that would fail without the internal {epibuffet} functions.

This PR will fix #229

I've also added a single place where we can place the explicit exports.

Need to do:

• [ ] also add the functions in https://github.com/R4EPI/msfmisc
• [ ] prune dependencies to those used by the sitrep package and the templates

Note: appveyor is currently failing because it's being a diva and doesn't want to build the package from source :roll_eyes:

[zkamvar]

I'm not sure why I closed this in February... It should be a relatively cromulent PR.