findCompression = function(compressionMethod) {
    for (var method in compressions) {
        if (!compressions.hasOwnProperty(method)) {
            continue;
        }
        if (compressions[method].magic === compressionMethod) {
            return compressions[method];
        }
    }
    return null;
}
Find a compression registered in JSZip.
@param {string} compressionMethod the method magic to find.
@return {Object|null} the JSZip compression object, null if none found.