Add files to run php56 tests inside a docker container

tests/dockerfiles/php56/1_build.sh

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+# Build an image.
+docker build --tag="php-curl-class/php56" .

tests/dockerfiles/php56/2_run.sh

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+# Run image to create container and attach to it.
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+set -x
+cd "${SCRIPT_DIR}/../../.."
+project_dir="${PWD}"
+
+docker run \
+    --interactive \
+    --mount "type=bind,src=${project_dir},dst=/data,readonly=true" \
+    --name=php56 \
+    --rm \
+    --tty \
+    "php-curl-class/php56" /bin/bash

tests/dockerfiles/php56/3_test.sh

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+# Run tests inside container.
+command=$(cat <<-END
+mkdir --parents "/tmp/php-curl-class" &&
+rsync --exclude=".git" --exclude="vendor" --links --recursive "/data/" "/tmp/php-curl-class/" &&
+cd "/tmp/php-curl-class" &&
+export TRAVIS_PHP_VERSION="5.6" &&
+(
+    [ ! -f "/tmp/.composer_updated" ] &&
+    composer --no-interaction update &&
+    touch "/tmp/.composer_updated" ||
+    exit 0
+) &&
+bash "tests/before_script.sh" &&
+bash "tests/script.sh"
+END
+)
+docker exec --interactive --tty "php56" sh -c "${command}"

tests/dockerfiles/php56/Dockerfile

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+FROM php:5.6-cli
+ENV DEBIAN_FRONTEND noninteractive
+
+RUN apt-get --assume-yes --quiet update
+
+RUN apt-get --assume-yes --quiet install git && \
+    apt-get --assume-yes --quiet install libpng-dev && \
+    apt-get --assume-yes --quiet install zip
+
+RUN curl --silent --show-error "https://getcomposer.org/installer" | php && \
+    mv "composer.phar" "/usr/local/bin/composer" && \
+    composer global require --no-interaction "phpunit/phpunit"
+
+RUN docker-php-ext-configure gd && \
+    docker-php-ext-install gd
+
+ENV PATH /root/.composer/vendor/bin:$PATH
+CMD ["bash"]