Plot images in existing canvases (fix #3)
Add new test functionality
Small cleanups to tile example
Add convenience functions for window management
Merge branch 'rsr/contrast'
Contrast GUI: fix inexact error for integer images
Work around SubArray limitations by taking the data
Small improvements to initialization, display, and callbacks of contrast GUI
Fix for sliders now returning floating point values (JuliaLang/Tk.jl@e5bb68fbba)
Don't let the contrast values cross