Add update_member and get_members_xlsx methods

[alistair0adams]

Added two methods

1. update_member() which will POST updated member data back to Spond
2. get_members_xlsx() which will download the Excel sheet that can be manually downloaded from the Spond website. This can easily then be converted into a Dataframe.

[elliot-100]

Thanks for this @alistair0adams .

Are you OK to add the missing return annotation? Should be JSONDict.

[alistair0adams]

JSONDict annotation added

[elliot-100]

Sorry @alistair0adams have been on other projects. Will try to test in next 1-2 weeks.