Basic SE-based morphological operators

Benchmark must cover image2d with rectangle (square) / diamond / disk / custom SE on a 20 Mpix image.

Add basic SE

• Disc
• Rectangle
• Diamond
• Oriented line

Erosion / Dilation

• Tests
• Documentation
• Benchmark

Structural Opening / Closing

• Tests
• Documentation
• Benchmark

Hit-or-miss

• Tests
• Documentation
• Benchmark

Morphological gradient (external / internal)

• Tests
• Documentation
• Benchmark

Black & White top-hat

• Tests
• Documentation
• Benchmark