drop ImageInTerminal

[t-bltg]

Fix #116, all tests pass locally.

Needs JuliaImages/ImageInTerminal.jl#71 and JuliaImages/XTermColors.jl#8.

Ping @johnnychen94 for review, since I cannot request for a review here (not a member of JuliaTesting org).

[oxinabox]

This PR would be much better if it was broken into two.
One which supports ImageInTerminals v0.5 and updates all reference images
and one containing all other changes.

[t-bltg]

This PR would be much better if it was broken into two.

Agreed, will split (EDIT: see #118).

[johnnychen94]

Maybe we'd just switch to XTermColors.ascii_show? For test utils like ReferenceTests, it actually doesn't make much sense to override the default display or Base.show methods -- it might have unexpected side-effects. For instance, if people use Documenter.doctest in test/runtests.jl, it will be ruined.

[t-bltg]

Maybe we'd just switch to XTermColors.ascii_show

This is very clever and benefits from the rework / splitting of ImageInTerminal 0.5 (credits to @johnnychen94 for the big picture):

1. it avoids ImageInTerminal side effects e.g. overriding Base.show;
2. it reduces dependencies, thus improving load times;
3. it solves the circular dependency at the origin of ReferenceTests is not compatible with ImageInTerminal 0.5.0 #116.

[johnnychen94]

Looks like we'd need to release JuliaImages/XTermColors.jl#8 (review) first

[johnnychen94]

@t-bltg let me know when you're ready for ReferenceTests v0.10 release.

[t-bltg]

When you want, so that we can go forward on JuliaImages/ImageInTerminal.jl#71.