Fix compilation with DMD 2.072.0

The following DMD PRs added more rigorous safety checks directly
affecting this project:
* dlang/dmd#5852 (fix Issue 15399 - unaligned pointers are not
  `@safe`) - triggered at line:
  https://github.com/kiith-sa/D-YAML/blob/v0.5.3/source/dyaml/emitter.d#L1011

* dlang/dmd#5940 (Unions may break immutability / unions with
  pointers are un-`@safe` ) - triggered at line:
  https://github.com/kiith-sa/D-YAML/blob/v0.5.3/source/dyaml/event.d#L230

* dlang/dmd#5876 (Casting from `void[]` to `T[]` is erroneously
  considered `@safe`) - triggered at line:
  https://github.com/kiith-sa/D-YAML/blob/v0.5.3/source/dyaml/loader.d#L186

* dlang/dmd#5860 (array.ptr in @safe code may point past end
  of array) - triggered at line:
  https://github.com/kiith-sa/D-YAML/blob/v0.5.3/source/dyaml/zerostring.d#L35

source/dyaml/emitter.d

@@ -54,7 +54,7 @@ class EmitterException : YAMLException
 private alias EmitterException Error;
 
 //Stores results of analysis of a scalar, determining e.g. what scalar style to use.
-align(4) struct ScalarAnalysis
+struct ScalarAnalysis
 {
     //Scalar itself.
     string scalar;

source/dyaml/event.d

@@ -227,8 +227,12 @@ Event scalarEvent(const Mark start, const Mark end, const Anchor anchor, const T
     result.value       = value;
     result.startMark   = start;
     result.endMark     = end;
+
+    () @trusted {
         result.anchor  = anchor;
         result.tag     = tag;
+    }();
+
     result.id          = EventID.Scalar;
     result.scalarStyle = style;
     result.implicit    = implicit[0];

source/dyaml/loader.d

@@ -179,7 +179,7 @@ struct Loader
          *
          * Throws:  YAMLException if yamlData contains data illegal in YAML.
          */
-        this(void[] yamlData) @safe
+        this(void[] yamlData) @trusted
         {
             try
             {

source/dyaml/zerostring.d

@@ -24,7 +24,7 @@ struct ZeroString(string TypeName)
         @disable int opCmp(ref ZeroString);
 
         ///Construct a string.
-        this(const string str) pure nothrow @safe
+        this(const string str) pure nothrow @trusted
         {
             if(str is null || str == "")
             {