String: Improved interface to allow chaining of init functions

For example; Str_Set(Str_Init(&str), "sometext");

doomsday/engine/api/dd_string.h

@@ -104,20 +104,20 @@ ddstring_t* Str_NewFromReader(Reader* reader);
  * Call this for uninitialized strings. Global variables are
  * automatically cleared, so they don't need initialization.
  */
-void Str_Init(ddstring_t* ds);
+ddstring_t* Str_Init(ddstring_t* ds);
 
 /**
  * Call this for uninitialized strings. Makes the string use standard
  * malloc for memory allocations.
  */
-void Str_InitStd(ddstring_t* ds);
+ddstring_t* Str_InitStd(ddstring_t* ds);
 
 /**
  * Initializes @a ds with a static const C string. No memory allocation
  * model is selected; use this for strings that remain constant.
  * If the string is never modified calling Str_Free() is not needed.
  */
-void Str_InitStatic(ddstring_t* ds, const char* staticConstStr);
+ddstring_t* Str_InitStatic(ddstring_t* ds, const char* staticConstStr);
 
 /**
  * Empty an existing string. After this the string is in the same

doomsday/engine/portable/src/m_string.c

@@ -99,19 +99,18 @@ static void allocateString(ddstring_t *str, size_t for_length, int preserve)
  * automatically cleared, so they don't need initialization.
  * The string will use the memory zone.
  */
-void Str_Init(ddstring_t *str)
+ddstring_t* Str_Init(ddstring_t* str)
 {
     if(!str)
     {
         Con_Error("Attempted String::Init with invalid reference (this==0).");
-        return; // Unreachable.
+        exit(1); // Unreachable.
     }
 
     if(!Z_IsInited())
     {
         // The memory zone is not available at the moment.
-        Str_InitStd(str);
-        return;
+        return Str_InitStd(str);
     }
 
     memset(str, 0, sizeof(*str));
@@ -120,25 +119,28 @@ void Str_Init(ddstring_t *str)
     str->memFree = Z_Free;
     str->memAlloc = zoneAlloc;
     str->memCalloc = zoneCalloc;
+    return str;
 }
 
 /**
  * The string will use standard memory allocation.
  */
-void Str_InitStd(ddstring_t *str)
+ddstring_t* Str_InitStd(ddstring_t* str)
 {
     memset(str, 0, sizeof(*str));
 
     // Init the memory management.
     str->memFree = free;
     str->memAlloc = malloc;
     str->memCalloc = stdCalloc;
+    return str;
 }
 
-void Str_InitStatic(ddstring_t* str, const char* staticConstStr)
+ddstring_t* Str_InitStatic(ddstring_t* str, const char* staticConstStr)
 {
     memset(str, 0, sizeof(*str));
     str->str = (char*) staticConstStr;
+    return str;
 }
 
 void Str_Free(ddstring_t* str)