* Adds startTupleField/startStructField, makes pattern in print targets less verbose
* Makes some enums into strings
* Start/finish renamed to begin/end
I feel bad changing this, but I don't know why I named them this way in the first place.
Begin/end is consistent with the json API, and with other APIs in the wild that follow this pattern.
Better to change now than later.
This commit allows using ZON (Zig Object Notation) in a few ways.
* `@import` can be used to load ZON at comptime and convert it to a
normal Zig value. In this case, `@import` must have a result type.
* `std.zon.parse` can be used to parse ZON at runtime, akin to the
parsing logic in `std.json`.
* `std.zon.stringify` can be used to convert arbitrary data structures
to ZON at runtime, again akin to `std.json`.
