* @enumTagName renamed to @tagName and it works on enums and
union-enums
* Remove the EnumTag type. Now there is only enum and union,
and the tag type of a union is always an enum.
* unions support specifying the tag enum type, and they support
inferring an enum tag type.
* Enums no longer support field types but they do support
setting the tag values. Likewise union-enums when inferring
an enum tag type support setting the tag values.
* It is now an error for enums and unions to have 0 fields.
* switch statements support union-enums
closes#618
* remove `@setGlobalAlign`
* add align keyword for setting alignment on functions and
variables.
* loads and stores use alignment from pointer
* memcpy, memset use alignment from pointer
* add syntax for pointer alignment
* slices can have volatile
* add u2, i2 primitives
* ignore preferred align and use abi align everywhere
* back to only having alignOf builtin.
preferredAlignOf is too tricky to be useful.
See #432. Partial revert of
e726925e80.
See #37