Swap "[]" and "{}" for denoting sets and lists in typestrings

[daboehme]

Python and JSON use "[]" for lists and "{}" for sets/dicts. Adiak does the opposite, which is confusing. Let's consider swapping it to align Adiak with existing practices.

[baallan]

This makes sense in principle, but it will be a breaking change for any downstream clients that have already assumed the prior delimiter syntax. Regarding ldms/adc work, I do not have any such clients, but rumors of other profiling tools adding adiak support do exist.

[baallan]

The other item that occurs to me about this is that sets/lists/etc can all be serialized/stored as arrays with an enum/string giving the semantics of the array (set, list, etc). Perhaps just expose this fact downstream instead of relying on someone depending on the delimiter type. Maybe this is a tool plugin-specific issue rather than an adiak issue?