cross-ci/build/mmd.js

`cross-ci` standardizes environment variables for CI. For example, your can simply use `BUILD_BRANCH` variable in all CI runners instead of `CIRCLE_BRANCH` in CircleCI or `TRAVIS_PULL_REQUEST_BRANCH` in Travis.

const docifyFolder = require('./docifyFolder');

exports.variableList = () => docifyFolder({
    folder: 'lib/var',
    concatBlock: () => '',
    concatListItem: (name) => '- [`' + name + '`](#' + name.toLowerCase() + ')\n',
});

exports.variables = () => docifyFolder({
    folder: 'lib/var',
    concatBlock: (name, src) => `#### \`${name}\`\n\n` + src + '\n\n\n',
    concatListItem: () => '',
});