`child::run` overrides the stdout config, so is misleading to to set it
differently beforehand. `child::run` uses `spawn()`, which inherits
stdin by default. So, no need to set stdin to default beforehand,
particularly when the spawned program is non-interactive.

Issue rustwasm#277 - Affects running login, pack, and publish on Windows.

`Command::new("npm")` launched `npm` with quotes, `"npm"`, causing a
run-time error on Windows. Now, `Command::new` is wrapped by
`child::new_command(program: &str)`. This prepends `cmd /c` to the
program name if `cfg!(windows)`.

See rustc: #42436, #42791, #44542

Windows fixes

This commit replaces the `slog` family of crates used by `wasm-pack`
with the `log` crate plus `env_logger`. This also means that by default
`wasm-pack` also won't create a `wasm-pack.log` file in the current
directory. Enabling logging will now be done through
`RUST_LOG=wasm_pack` instead of `-v` flags.

Closes rustwasm#425

Alexcrichton log

v0.6.0

I believe the older code has something wrong so it install wasm-bindgen
from cargo, but now it can download
the prebuilt version.

fixes rustwasm#447

because the assert commaned seems to capture stdout in err string,
work around the test faing by double the log counts