fixed_regex_linter could optionally skip special-free strings

[MichaelChirico]

Some users prefer the conciseness of grepl("xxx", str) to grepl("xxx", str, fixed = TRUE).

I can't think of a snappy name for the argument right away :)

[AshesITR]

Wouldn't these users just disable the linter?

[MichaelChirico]

to clarify I mean grepl("[$]", x) still lints because it uses regex specials. I was thinking running grepl on the string against itself world work