zulip_tools.py: Add `purge_caches()` function.
zulip_tools.py: Add `purge_caches()` function.

This function can be used for purging unused cache directories.

hackerkid/zulip,showell/zulip,shubhamdhama/zulip,punchagan/zulip,Galexrt/zulip,dhcrzf/zulip,synicalsyntax/zulip,amanharitsh123/zulip,rht/zulip,tommyip/zulip,brockwhittaker/zulip,zulip/zulip,hackerkid/zulip,andersk/zulip,kou/zulip,Galexrt/zulip,eeshangarg/zulip,dhcrzf/zulip,eeshangarg/zulip,andersk/zulip,verma-varsha/zulip,shubhamdhama/zulip,punchagan/zulip,brainwane/zulip,synicalsyntax/zulip,showell/zulip,rht/zulip,zulip/zulip,timabbott/zulip,mahim97/zulip,verma-varsha/zulip,brockwhittaker/zulip,showell/zulip,punchagan/zulip,dhcrzf/zulip,brainwane/zulip,showell/zulip,andersk/zulip,verma-varsha/zulip,timabbott/zulip,synicalsyntax/zulip,timabbott/zulip,andersk/zulip,brockwhittaker/zulip,shubhamdhama/zulip,brockwhittaker/zulip,tommyip/zulip,Galexrt/zulip,timabbott/zulip,brainwane/zulip,verma-varsha/zulip,dhcrzf/zulip,eeshangarg/zulip,timabbott/zulip,timabbott/zulip,zulip/zulip,hackerkid/zulip,rishig/zulip,amanharitsh123/zulip,amanharitsh123/zulip,rishig/zulip,kou/zulip,mahim97/zulip,synicalsyntax/zulip,showell/zulip,punchagan/zulip,synicalsyntax/zulip,dhcrzf/zulip,amanharitsh123/zulip,brainwane/zulip,verma-varsha/zulip,jackrzhang/zulip,rishig/zulip,zulip/zulip,tommyip/zulip,hackerkid/zulip,jackrzhang/zulip,dhcrzf/zulip,eeshangarg/zulip,punchagan/zulip,brockwhittaker/zulip,rht/zulip,tommyip/zulip,punchagan/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip,timabbott/zulip,kou/zulip,kou/zulip,andersk/zulip,hackerkid/zulip,mahim97/zulip,Galexrt/zulip,rht/zulip,shubhamdhama/zulip,tommyip/zulip,rishig/zulip,rishig/zulip,Galexrt/zulip,jackrzhang/zulip,andersk/zulip,amanharitsh123/zulip,zulip/zulip,jackrzhang/zulip,brainwane/zulip,tommyip/zulip,shubhamdhama/zulip,shubhamdhama/zulip,synicalsyntax/zulip,verma-varsha/zulip,rht/zulip,dhcrzf/zulip,brockwhittaker/zulip,kou/zulip,brainwane/zulip,Galexrt/zulip,mahim97/zulip,mahim97/zulip,jackrzhang/zulip,brainwane/zulip,kou/zulip,rishig/zulip,punchagan/zulip,andersk/zulip,hackerkid/zulip,jackrzhang/zulip,mahim97/zulip,kou/zulip,Galexrt/zulip,rishig/zulip,hackerkid/zulip,rht/zulip,jackrzhang/zulip,eeshangarg/zulip,rht/zulip,showell/zulip,showell/zulip,shubhamdhama/zulip,amanharitsh123/zulip,eeshangarg/zulip,synicalsyntax/zulip,tommyip/zulip