Reverse inplace concatentation operator =.. #71
Description
Reverse inplace concatenation operator =.. like a =.. b means a = b .. a (a ..= b means a = a .. b)
The = would represent where the new string will go.
.. is a binary operator so no backcompat issues.
This is likely not going to be implemented for a while - it probably won't be implemented at all due to its sheer weirdness.
(..= isn't even implemented - it needs syntax desugaring (#40) which isn't even started)
Requires #40