Add newlines after standalone attributes

[whitequark]

The quote crate currently outputs the following rather pathological header, which rustfmt leaves nearly verbatim:

# ! [ doc = "Peripheral access API for TM4C1294NCPDT microcontrollers (generated using svd2rust v0.7.0)" ] # ! [ deny ( missing_docs ) ] # ! [ deny ( warnings ) ] # ! [ feature ( const_fn ) ] # ! [ no_std ]extern crate cortex_m ;

The whitespace inside attributes is handled by #984 (but this could provide another testcase), whereas the newline after the attribute doesn't seem to be mentioned anywhere.

[nrc]

I think we do insert newlines in some cases, Rustfmt is probably tripping up somewhere gives up formatting, thus not inserting the newlines.

[valpackett]

I'd actually like to have an option to not insert newlines into e.g.

#[cfg(feature = "filesystem")] use fuse::*;

[topecongiro]

Closing as this is fixed on the current master.