More fixes for Worksheet.update argument ordering & single cell updating (i.e. now Worksheet.update_acell)

[alexmalins]

Fixes similar to #1431 for docs, a docstring and a test.

• Worksheet.update default argument ordering is now Worksheet.update(<values>, <range name>, ...
• Single cell updating uses the Worksheet.update_acell method now

[alifeee]

hey! thanks for this change !! :)

it is very helpful. I am not sure of the best way of keeping the code and the docs in sync 🤔

I will let @lavigne958 merge :)

[lavigne958]

hey! thanks for this change !! :)

it is very helpful. I am not sure of the best way of keeping the code and the docs in sync 🤔

there isn't in small projects like ours 😞 we must think about updating it every time we change something.

I will let @lavigne958 merge :)
will do !