…y someone else

…stats=True option to return some stats and an outcome ('sucess' or other, atm)

…improve the subclassing of logging. at the moment it is not doing much, but have left the SDKLogger functionality in there in case there are some broad changes that are best made in that object.

* replaced print()s with logging

* log certain exceptions using logger
* remove redundant log for folder exists, comes up all the time in my logs and feels not useful

…here is actually a callback specified

* `chunks_num` the new name
* set `chunk_size` once, it doesn't change for a _download_whole()

- allow checksum verification for download
- permit write files to temp file name, off by default
- better download outcome returns (lines 216-231) arguably these should just be Exceptions...

download.py - annoying doubled up code from years ago - deprecated