src: format source code with clang-format

Apply the formatting rules from the previous commit and reformat all
source files in the src/ directory.  From this commit forward,
`clang-format` is the ultimate authority on formatting issues.

Fixes node-forward/node#2.

R=@indutny?

For the record:

> No effort has been made to tweak the formatting rules to make them
> adhere closer to the current style because of compatibility with
> clang-format 3.4.  It's old but prevalent and has only limited
> support for tweaking built-in rules.