Increase default stack size to 2MB with opt-out available

[ian-h-chamberlain]

Fix / workaround for issue seen in #56

Add a Cargo feature to allow users to set the stack size if desired, but
default to 2MB to handle more use cases.

@Meziu @AzureMarker what do you think of this approach? Open to alternate naming suggestions on the cargo feature as well, I don't love big-stack but wanted to post this as a starting point for discussion.

Another approach I considered was exporting a macro like

ctru::stack_size!(64 * 1024);

But it felt a bit clunky and would require every user to set this if their program had large enough stacks. I would imagine that custom stack size is a pretty advanced use case (assuming we pick a good default) so I think it should still be possible for users to opt-out of the default, but I'm not sure of another way besides a Cargo feature.

[AzureMarker]

Thanks for fixing this!!

[AzureMarker]

The feature name seems good enough to me. We could in the future have both the feature and a macro to set the stack size.

[ian-h-chamberlain]

Another option I considered was something like custom-stack-size and invert the semantics – i.e. configure this size when #[cfg(not(feature = "custom-stack-size"))]. But the guidance from documentation kidn of seems to discourage this (https://doc.rust-lang.org/cargo/reference/features.html#feature-unification):

A consequence of this is that features should be additive. That is, enabling a feature should not disable functionality, and it should usually be safe to enable any combination of features. A feature should not introduce a SemVer-incompatible change.

So I guess this can be good enough for now.