inform() does not include trailing newlines in condition messages

[lionel-]

Causes trouble when message is captured, cf discussion in r-lib/usethis#937.

[krlmlr]

I wonder if inform() should return invisibly too.

f <- function() {
  rlang::inform("hi")
  rlang::inform("ho")
}
f()
#> hiho
#> NULL

^{Created on 2019-12-30 by the reprex package (v0.3.0)}