Inconsistent behaviour between `lestrade` and `sherlock`

[Torvaney]

highlight::sherlock returns a new function, whereas highlight::lestrade returns data(?).

This behavour is inconsistent (and also means the sherlock example in README.md is incorrect):

# Works
highlight::highlight(file = "test.R", detective = highlight::lestrade)

# Doesn't work
highlight::highlight(file = "test.R", detective = highlight::sherlock)
#> Error in UseMethod("filter_") : 
#>   no applicable method for 'filter_' applied to an object of class "function"

# Works
highlight::highlight(file = "test.R", detective = highlight::sherlock())