* Fix assertion failure when switching on type.
   Closes #310
 * Update zig build system to support user defined options.
   See #204
 * fmt.format supports {sNNN} to set padding for a buffer arg.
 * add std.fmt.bufPrint and std.fmt.allocPrint
 * std.hash_map.HashMap.put returns the previous value
 * add std.mem.startsWith