Add a script to build docs with all features enabled

#!/bin/bash

set -e

export CARGO_TARGET_DIR=target

for toml in $(find . -maxdepth 2 -name "Cargo.toml"); do

    cargo update --manifest-path $toml || true

    features=$(cargo read-manifest --manifest-path $toml | jq -r '.features|keys|join(" ")')

    cargo doc --verbose --no-deps --manifest-path $toml --features "$features"

done