spec: bytes data type (#161)
spec: bytes data type (#161)

* spec: bytes data type

This change adds initial specification of the bytes data type
following length discussion in #112.
It also explains the implementation-dependent encoding of
text strings, and the \u and \U escapes.

More will follow, but let's get the easy parts out of the way first.

Updates #112
bazelbuild/starlark,bazelbuild/starlark