Disposable issues discussion

[Bykiev]

@JimBobSquarePants , hi, I've used IDisposableAnalyzers to detect some issues. There are some interesting issues which should be fixed.

1. FontReader class has a local variable stream, which is disposed in the constructor. I believe it's not correct and FontReader class shouldn't dispose it at all, instead FontReader class should implement IDisposable to dispose created MemoryStream.
   Small code snippet of proposed changes:

private readonly bool disposable = false;
...
else if (version == 0x774F4632)
{
  ....
   disposable  = true;
   this.stream = decompressedStream;
}

public void Dispose()
{
   if (disposable)
     this.stream.Dispose();
}

2. BigEndianBinaryReader right now has an empty Dispose method, because of this the using statement is not used when created an instance. To be more consistent it'll be good to wrap all instances in using statement. What do you think?

I've created a PR #411