Add is_zero method to Zero
Allow customization of indent offset
Use `///` doc-comment form instead of `/** */`
Minor style improvements for test functions

Use argument pattern-matching for test_division_rule and remove visibility specifier for test_signed
Add Bitwise, Bounded, Primitive, and PrimitiveInt traits
Add Int, Uint and Float traits for primitive numbers
Add BitCount trait
Fix failing test
Offer a hint on some unresolved imports

I didn't know how to use "use" initially, and an error message like this would
have solved quite a bit of frustration. I think this properly handles cases
where it's not appropriate but I'm not sure.
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Combine PrimitiveInt, Int, and Uint traits into one single trait

Having three traits for primitive ints/uints seemed rather excessive. If users wish to specify between them they can simply combine Int with either the Signed and Unsigned traits. For example: fn foo<T: Int + Signed>() { … }
Fix typo
Add Orderable trait

This is a temporary trait until we have default methods. We don't want to encumber all implementors of Ord by requiring them to implement these functions, but at the same time we want to be able to take advantage of the speed of the specific numeric functions (like the `fmin` and `fmax` intrinsics).
Add mul_add and next_after methods to Float
tutorial: rework the section on destructors

This removes the comparison to manual memory management examples,
because it requires too much existing knowledge. Implementing custom
destructors can be covered in the FFI tutorial, where `unsafe` is
already well explained.
tutorial-ffi: add example of a custom destructor
rt: Set the stack depth limit to 1GB. Abort on error.

People hit the recursion depth limit too often, it's not possible
to unwind reliably from out-of-stack.

Issues #3555, #3695
core: Move mkdir_recursive from rustpkg into core::os

mkdir_recursive creates a directory as well as any of its
parent directories that don't exist already. Seems like a useful
thing to have in core.
Add additional constants to primitive floating point numbers

These follow the values defined in the C99 standard
Rename `nextafter` to `next_after` to match method name in Float