Fix the Continuous Integration

[eisterman]

I've noticed that the CI have a problem with the command cargo clippy --all -- -D warnings (CLIPPY=yes). The problem as seen in https://travis-ci.org/bheisler/RustaCUDA/jobs/630513201#L349 was some warning arose from clippy:

• clippy::needless-doctest-main
• mem::uninitialized is now deprecated in favour of mem::MaybeUninit
• clippy::missing-safety-doc

So I've made this pull request to fix all this problem. The solutions used are:

• Remove the needless fn main() {} from all the documentation
• Replace std::mem::uninitialized() with std::mem::MaybeUninit::uninit().assume_init()
• Fix the wrong /// # Safety: comment removing the colon ( /// # Safety )
• Write the /// # Safety for 4 unsafe function really missing it

PS: I have not opened an issue given the nature of the problem, strictly linked to the way in which continuous integration has been programmed.

[eisterman]

I've added a commit to fix some space artifact left by Visual Studio Code.

[bheisler]

Hi, thanks for the pull request! Unfortunately, your changes to mem::uninitialized will conflict with another PR that I just merged; would you mind reverting (or rebasing out) that change?

[eisterman]

Is this ok?

[bheisler]

Looks good to me. Thanks!