Return context of multiline function signatures
Return context of multiline function signatures

`contextstr` for function, trait and struct definitions now looks ahead
for opening brace and replaces all whitespace for single spaces.

Fixes #512

alkama/racer,birkenfeld/racer,hotpxl/racer,racer-rust/racer,jaxx/racer,phildawes/racer,sliz1/racer,pmarcelll/racer