Add variable length 7-bit integer encoder/decoder
Add variable length 7-bit integer encoder/decoder

This will be used when emitting field 32-bit integers into field
records, which are likely to be small and benefit from this kind
of encoding. These can potentially also be used in other places
where we emit integer constants to save space.

khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift