Internal: Run `lintr` over the project and amend code presentation accordingly

[francisbarton]

PR #126 should close this

[ThomUK]

Human Input Needed

This issue references PR #126 as already containing the fix. Please confirm:

1. Was PR Run lintr over the project and amend code presentation accordingly #126 merged? If so, this issue can be closed.
2. If the lintr work still needs to be done, please describe the current state and which files need attention.