New hcat and vcat for drawings

[davibarreira]

This is a small contribution, but I think it might be quite useful. It overloads the Base.hcat and Base.vcat to work with figures. So one can easily concatenate figures in Luxor.

I've implemented the two functions and a set of tests.

Here is an example.

    d1 = Drawing(200,100,:svg)
    origin()
    circle(O,60,:fill)
    finish()

    d2 = Drawing(200,200,:svg)
    rect(O,200,200,:fill)
    finish()
    hcat(d1,d2; hpad=10, valign=:top, clip = true)

[cormullion]

Cool! Just SVG or any format?

[codecov]

Codecov Report

Merging #210 (f2426d1) into master (1473624) will increase coverage by 0.19%.
The diff coverage is 92.59%.

❗ Current head f2426d1 differs from pull request most recent head e73caff. Consider uploading reports for the commit e73caff to get more accurate results

@@            Coverage Diff             @@
##           master     #210      +/-   ##
==========================================
+ Coverage   70.85%   71.05%   +0.19%     
==========================================
  Files          33       33              
  Lines        5919     5973      +54     
==========================================
+ Hits         4194     4244      +50     
- Misses       1725     1729       +4     

Impacted Files	Coverage Δ
src/basics.jl	92.17% <92.59%> (+0.12%)	⬆️

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[davibarreira]

I've tried with d1 = Drawing(200,100,:png) and got an error saying surfacetype pngis not supported. Useimage instead.. Don't know exactly why. The function I've implemented is quite simple, and I thought it would work with png. But I guess not.

[davibarreira]

@cormullion, is it possible to do a placeimage with d as png? This is what is causing the error. I don't know how to solve it, unless by saving the png as a file and using readpng as in the docs.

[cormullion]

You can do that kind of thing if you have extracted the image_as_matrix before you finish().

Perhaps this PR should somehow be restricted to SVG+SVG only; otherwise it will be difficult to hcat, say, a PNG and an SVG, or a PNG and a EPS.

[davibarreira]

Done! Added a new line in the code to check that the surfacetype is svg, and also specified in the docstring :)

[cormullion]

Awesome! Thanks!

[cormullion]

I added an example to the docs for you:

http://juliagraphics.github.io/Luxor.jl/dev/howto/createdrawings/#Concatenating-SVG-drawings

[davibarreira]

Has this been released?

[cormullion]

Not yet. Luxor's release schedule is vaguely monthly, so perhaps I should do one soon...