this affects the scanner/parser and makes it produce signed ints rather than
uints, and so it affects all code that is expecting unsighed ints to come out of
the parser.
This commit refactors the profile and bitmap attribute stores so
that they share the same code. There is a new `AttrStore` which
associates key/value pairs with a `uint64` identifier.
The previous JSON encoding has been fixed to use protobufs which
fixes encoding issues for int64.
