Declaration Tags Using `@` Syntax

[ephf]

I am thinking about adding tags either through # or @ syntax, (leaning more towards @ as # may be designated for macros).

type i8 = extern int int8_t @{ alias: b }
type i16 = extern int int16_t @{ alias: s }
type i32 = extern int int32_t @{ alias: i }
type i64 = extern int int64_t @{ alias: l }

I use the brackets because I also wanted to add internal type overrides like Slice and Range etc

struct MyRange @{ Range } { /* ... */ }