fix Issue 13664 - Grammar does not allow @<template_instance> UDAs
Added new type alias syntax as a preference

Added elaboration based on comments received

Fix syntax errors
macros.ddoc
Merge pull request #701 from aG0aep6G/macros.ddoc

macros.ddoc
Merge pull request #683 from 9rnsr/fix13664

Issue 13664 - Grammar does not allow @<template_instance> UDAs
Merge pull request #682 from JinShil/patch-1

Added new type alias syntax as a preference
unions may not have postblits, destructors, or invariants
Merge pull request #702 from WalterBright/unions

unions may not have postblits, destructors, or invariants