Include new operators from R >=v4.1

[matt-dray]

Allow for the new pipe |> and 'lambda' anonymous function syntax \() to be detected. The latter is more tricky than e.g. function(x), of course.

[matt-dray]

r"{}", %||%.

[matt-dray]

|> is going to be troublesome because:

substitute(x |> print())
# print(x)

[matt-dray]

gram.y here: https://github.com/wch/r-source/blob/trunk/src/main/gram.y