WIP: refactor: migrate from stack allocations to dynamic allocations

[AdrianDC]

A refactoring based on @holmanb initial dynamic allocations commits, with:

• Multiple refactoring and cleanups
• Simplification of the allocations to avoid allocating every simple struct or array of text that are already dynamically allocated
• Some fixes resolving memory leaks that were introduced

Only the earliest two commits are on review in the PR, until the other ones are merged.

Further work must be done to simplify and cleanup the sources.

[annacrombie]

First off, this was actually the original way plot was implemented, but I refactored it last april (https://github.com/annacrombie/plot/commit/e4b2d91173f531ddf30b9ada540887c155c8562b).

My reasons to use only stack allocation were robustness and speed. If you never call alloc, you can't have a memory leak. I don't really see a reason to switch back to heap allocation, since plot doesn't need much memory anyway. Please let me know your thoughts though

[holmanb]

My original reasoning for doing this was that when growing the plot to larger fixed size bounds (see #11), the stack starts to grow and I was having issues with stack sizes if I remember correctly.

In my project I'm temporarily using the default plot bounds behaviour, but I do plan on eventually switching back to the -b option for fixed sizes and I expect the bounds to require larger values (10k, maybe higher). I honestly didn't understand the plot code very well when I started looking for a way to get larger fixed sizes, so I'm sure somebody with a better understanding of plot's code might have better ideas than me.

[annacrombie]

The bounds represent the minimum and maximum values in the data so that it can be scaled to the correct range (based on the plot dimensions). Modifying values of bounds should not affect the memory usage. The only thing that would require a lot of memory would be making the plot dimensions very large. Since this tool is meant to format output for display on a terminal, which almost never has a very big resolution (my full-screen terminal is only 170x48), I feel comfortable putting a hard limit on the plot dimensions. Users who really need huge text plots can feel free to modify the MAX_HEIGHT / MAX_WIDTH an recompile, possibly even allocating the plot struct dynamically if stack space is an issue.

[AdrianDC]

Will close the PR within the next weeks.