Add support for thirdparty libraries with UMD wrappers - fixes #420

using a config option to determine whether to wrap a thirdparty library in a define block (#420).
once this has been merged across https://github.com/BladeRunnerJS/fell/tree/brjs-umd-wrapper-support, https://github.com/BladeRunnerJS/topiarist/tree/brjs-umd-wrapper-support, https://github.com/BladeRunnerJS/emitr/tree/brjs-umd-wrapper-support and https://github.com/BladeRunnerJS/browser-modules/tree/brjs-umd-wrapper-support all need to be merged in to the `gh-pages` branch in each repo.