remove bash 4 requirement

[thobianchi]

This removes the requirements to bash4.
I substituted readarray with a while loop and associative array with dynamic variable names.

I tested this on:

$ bash --version
GNU bash, version 3.2.57(1)-release (x86_64-suse-linux-gnu)
Copyright (C) 2007 Free Software Foundation, Inc.

[boomskats]

Sorry @thobianchi, I've literally just seen this!

I'll run some tests over the weekend and merge it if it performs comparatively well with ~1k sessions. Nice work.

[boomskats]

'over the weekend' = 'exactly 1 year later'

Thanks for the fix @thobianchi, works and performs well