Magick.NET 7.3.0.0

Breaking changes in Magick.NET:

• Removed FileSize property of MagickImage.

Changes in Magick.NET:

• Added ColorSpace.LinearGray.
• Fixed reading of non-seekable Stream reported in #141.

Related changes in ImageMagick since the last release of Magick.NET:

• Fixed numerous memory leaks (reference https://github.com/ImageMagick/ImageMagick/issues).
• Fix possible stack overflow in WEBP reader (reference ImageMagick/ImageMagick#907)

Library updates:

• ImageMagick 7.0.7.21