normalize dataset paths

[jheeffer]

Path normalization was included in the original PoC but was removed at some point.

This allows user to specify dataset path in several ways:

path/to/dataset/datapackage.json
path/to/dataset/
path/to/dataset

Please return it or give reasons for removing it

	function getDatapackagePath(path) {	
		if (!path.endsWith("datapackage.json")) {
			if (!path.endsWith("/")) {
				path = path + "/";
			}
			path = path + "datapackage.json";
		}
		return path;
	}

	function getBasePath(datapackagePath) {
		const dpPathSplit = datapackagePath.split("/");
		dpPathSplit.pop();
		return dpPathSplit.join("/") + "/";
	}

	const 
		datapackagePath    = getDatapackagePath(path),
		basePath           = getBasePath(datapackagePath);

https://github.com/jheeffer/ddfcsv-reader/blob/master/ddfcsv.js#L44-L58