Add a script to build docs with all features enabled

build_docs.sh

+#!/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