Inlining doesn't work properly with include style macros

[jethrogb]

See jethrogb/rust-reduce#8

[TedDriggs]

Hmm, I'm not sure how best to do this; are the include macros the only way this can happen?

[bjorn3]

Other than proc macros I think the include macros are the only way this can happen. There was a proposal to add a #[doc] variant that reads from a file, but I don't think it has been accepted.