Customise config

[SaranjeetKaur]

This pull request adapts the code to use a specified config. It also provides instructions on how to update the config. If no config is specified, then it will take the default config. But if you want to use a different config then it is possible to do so by ediitng the values under "production" field in the inst/config/config.yml file.

Fixes #91 #98

Some housekeeping checks

• All ok when you run devtools::check() after the changes you have made?
• Have you updated the .Rd files using devtools::document()?
• If there were changes to README.Rmd, did you build and render it using devtools::build_readme()?
• If you added a new function or changed an existing function, have you created a (or updated an existing) unit test for it using usethis::use_test()?

[SaranjeetKaur]

/style

[SaranjeetKaur]

Closing this with a different implementation in #116