color: refactor parse_attr

color: refactor parse_attr

The list of attributes we recognize is a bit unwieldy, as we
actually have two arrays that must be kept in sync. Instead,
let's have a single array-of-struct to represent our
mapping. That means we can never have an accident that
causes us to read off the end of an array, and it makes
diffs for adding new attributes much easier to read.

This also makes it easy to handle the "no" cases without
having to repeat each attribute (this shortens the list,
making it easier to read, but also also cuts the size of our
linear search in half). Technically this makes it impossible
for us to add an attribute that starts with "no" (we could
confuse "nobody" for the negation of "body"), but since this
is a constrained set of attributes, that's OK.

Since we can also store the length of each name in the
struct, that makes it easy for us to avoid reading past the
"len" parameter given to us (though in practice it was not a
bug, since all of our current callers are interested in a
subset of a NUL-terminated buffer, not a true undelimited
range of memory).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>