Tk canvas backend

[josepegea]

This adds a new backend to draw plots interactively using Ruby/Tk.

See the examples/tk_canvas_wrapper folder for details about how to use.

I wrote this backend in order to be able to use rubyplot with TkComponent and TkInspect, 2 gems I'm building to make it easier to work with GUIs in Ruby.

I would love to have this code merged into the main branch so I can have a stable version of rubyplot as a dependency, instead of a fork.

Thanks for your work in rubyplot, BTW!

[kojix2]

Yes. I want a way to draw a plot in tk.
You can use Plotchart in Ruby/Tk. However, libraries other than Plotchart are required.

[kojix2]

I hope this pull request will not be abandoned for a long time.

[josepegea]

Well, we could use a similar setup with putting the requiremente for gr and magick in the Gemfile instead of the gemspec and load them conditionally file so you can use the gem just with the backends you want and not forcing you to install external libs you're not going to use.

However, given the lack of response, I don't know how well that change would be accepted. Let's wait some days more.

If not, you can always use my fork, if needed. It's already working for me with Ruby/Tk