Add column header for info fibres, and add tabs between fields

Mohammed Bilal Akhtar requested to merge mbakhtar/KOS:minor-column-change into master

All other fields seem to closely mimic the output of info threads. I couldn't find a python API way to retrieve the inferior name, so that field (and others, like the names/values of function parameters) are missing.

One way to address this gap: we could just parse the output of bt and fill it in info fibres. But at the moment we just use the python API's functions/classes in inspecting things instead of parsing gdb output.

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