Run cargo fmt and remove warnings

There is still a warning in render.rs:

warning: calls to `std::mem::drop` with a reference instead of an owned value does nothing
   --> src\pipeline\subcommands\render.rs:153:9
    |
153 |         drop(&self.writer);
    |         ^^^^^------------^
    |              |
    |              argument has type `&PngWriter<'_>`
    |
    = note: use `let _ = ...` to ignore the expression or result
    = note: `#[warn(dropping_references)]` on by default

nus-vv-streams / vvtk

Run cargo fmt and remove warnings #35