Use a FileReader to handle music resources and audio decoding

Instead of the previous method where there'd be a filename and offset, and/or a
memory pointer, this uses a class to access resource data regardless of its
underlying form.

src/files.cpp

@@ -527,3 +527,59 @@ char *MemoryReader::Gets(char *strbuf, int len)
 {
 	return GetsFromBuffer(bufptr, strbuf, len);
 }
+
+//==========================================================================
+//
+// MemoryArrayReader
+//
+// reads data from an array of memory
+//
+//==========================================================================
+
+MemoryArrayReader::MemoryArrayReader (const char *buffer, long length)
+{
+    buf.Resize(length);
+    memcpy(&buf[0], buffer, length);
+    Length=length;
+    FilePos=0;
+}
+
+MemoryArrayReader::~MemoryArrayReader ()
+{
+}
+
+long MemoryArrayReader::Tell () const
+{
+    return FilePos;
+}
+
+long MemoryArrayReader::Seek (long offset, int origin)
+{
+    switch (origin)
+    {
+    case SEEK_CUR:
+        offset+=FilePos;
+        break;
+
+    case SEEK_END:
+        offset+=Length;
+        break;
+
+    }
+    FilePos=clamp<long>(offset,0,Length-1);
+    return 0;
+}
+
+long MemoryArrayReader::Read (void *buffer, long len)
+{
+    if (len>Length-FilePos) len=Length-FilePos;
+    if (len<0) len=0;
+    memcpy(buffer,&buf[FilePos],len);
+    FilePos+=len;
+    return len;
+}
+
+char *MemoryArrayReader::Gets(char *strbuf, int len)
+{
+    return GetsFromBuffer((char*)&buf[0], strbuf, len);
+}