Specify the handling of unrepresentable bounds

[jasonyu1996]

[Mingkai-Li]

See also: issue 5 from another repo, which contains some previous discussion about the capability compression problem.

[Mingkai-Li]

Also, is it better to have uncompressed capabilities in the register file, and only compress them in store operations?

Doing this would significantly reduce the number of exceptions caused by unrepresentable bounds, since most of the instructions, which only manipulate capabilities in the register, won't have any problem of unrepresentable bounds. And the problem is delayed until the store operations only, i.e., when calling STC.