Add wrapper for cairo_recording_surface_ink_extents()

[hustf]

Ref. #355

modified: samples/Samples.md Include sample_record_inkextents
new file: samples/sample_record_inkextents.jl
new file: samples/sample_record_inkextents.png
modified: src/Cairo.jl Add ink_extents

[codecov]

Codecov Report

Merging #356 (5cb5ba8) into master (2b7185c) will increase coverage by 0.30%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #356      +/-   ##
==========================================
+ Coverage   92.14%   92.44%   +0.30%     
==========================================
  Files           1        1              
  Lines         560      596      +36     
==========================================
+ Hits          516      551      +35     
- Misses         44       45       +1     

Impacted Files	Coverage Δ
src/Cairo.jl	92.44% <100.00%> (+0.30%)	⬆️

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[hustf]

As per @cormullion comment elsewhere: The only test so far follows the existing setup: A 'sample' file is included in 'runtests'. The test checks that an image file was produced. We could extend this to check pixel counts, but I am not sure if that would be a good test of weak points in this case. Difficult tests would include

• large variation of scales
• extending the canvas from positive to negative
• drawing shapes with non-trivial bounding boxes

But in these cases, we would be testing Cairo itself, not this wrapper.