Clone arguments before adding default properties

[fastfedora]

Prevents the client library from modifying the options argument during function calls, to allow the options object to be reused on future function calls. Uses a clone of the options instead to enhance with any additional properties that the internal code needs.

Note this uses a simplified version of clone with only the features required for this fix to minimize the size of the library.

Fixes #67

[tomhazledine]

Thanks for the detailed issue and fix, @fastfedora. Much appreciated 👍