Add new macros to allow assertions with custom exit code

[xxuejie]

This change adds 2 new macros & 1 utility functions, that allows one to set the return error code first, then runs assertions in Rust.

This allows us to get the benefit of both worlds: we could use assertion lines with decent debug message outputs, while at the same time we can also customize final exit code.

[XuJiandong]

It's better to add following:

1. Option's expect
2. macro assert_ne!
3. Result's expect_err

[xxuejie]

Done

[mohanson]

https://github.com/rust-lang/rust/blob/master/library/core/src/macros/panic.md#current-implementation

If the main thread panics it will terminate all your threads and end your program with code 101.

It's better to keep Rust's conventions

[xxuejie]

https://github.com/rust-lang/rust/blob/master/library/core/src/macros/panic.md#current-implementation

If the main thread panics it will terminate all your threads and end your program with code 101.

It's better to keep Rust's conventions

If you look at it, ckb-std already returns -1 when panic happens, which is different than Rust's convention. In addition, it is documented as "current implementation", not necessarily a convention.