add gif function

[johnnychen94]

Originally proposed in #22 (comment). This is a simple and yet powerful alternative to #29 for 3d image.

Example:

using ImageShow, TestImages, ImageTransformations

# 3d image
ImageShow.gif(testimage("mri-stack"))

# 2d images
toucan = testimage("toucan") # 150×162 RGBA image
moon = testimage("moon") # 256×256 Gray image
ImageShow.gif([toucan, moon])

# a do-function version
img = testimage("cameraman")
ImageShow.gif(-π/4:π/16:π/4]; fps=3) do θ
    imrotate(img, θ, axes(img))
end

• requires pass extra save_stream keywords to image2wand JuliaIO/ImageMagick.jl#199 (ImageMagick >= v1.2.0)
• need test

[codecov]

Codecov Report

Merging #30 (2fe3bc5) into master (48ababc) will increase coverage by 3.11%.
The diff coverage is 92.85%.

❗ Current head 2fe3bc5 differs from pull request most recent head 29afd4a. Consider uploading reports for the commit 29afd4a to get more accurate results

@@            Coverage Diff             @@
##           master      #30      +/-   ##
==========================================
+ Coverage   89.47%   92.59%   +3.11%     
==========================================
  Files           3        4       +1     
  Lines          76      108      +32     
==========================================
+ Hits           68      100      +32     
  Misses          8        8              

Impacted Files	Coverage Δ
src/ImageShow.jl	40.00% <ø> (ø)
src/compat.jl	50.00% <50.00%> (ø)
src/gif.jl	95.83% <95.83%> (ø)
src/showmime.jl	96.10% <100.00%> (+1.90%)	⬆️

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[timholy]

What do you see as the main benefit/different in the function-call vs macro form?

[johnnychen94]

No actual difference; I thought making it a macro is a kind of visual sign to indicate users that this @gif macro is only for "interactive" usage.

[ashwanirathee]

@johnnychen94 Is it possible as of now to show gif properly in ImageInTerminal.jl . Last I tried,it showed the gif as array of images one after another in column..

[johnnychen94]

ImageInTerminal does not understand GIF encoding, so I don't think it's possible as of now. JuliaImages/ImageInTerminal.jl#45 could possibly support it.

This PR is not released yet, I'm working on #29 now and plan to release both as ImageShow v0.3.0