Rclone 1.53.3 memory (leak?) problem

Hi @ncw

I tried it (git clone + docker build on the fix-azureblob-memory branch) and it works.

Just to compare, syncing the same data into an empty azureblob storage, docker stats on version 1.52.3 would report memory use of 261MB / 500MB
docker stats with the fix reports 278 MB / 500 MB, so in par with 1.52.3

Hopefully they will merge the fix soon.