Refine intra-doc links

[tranzystorekk]

A few changes to make documenting code with links simpler and more uniform.

Highlights:

• Make some common stdlib traits into links, e.g. IntoIterator
• Add links to docs for free functions
• Use module paths uniformly in links (instead of html paths)
• Link to slice::sort* methods in docs for sorting functions

[phimuemue]

Thanks for the cleanups - better docs are always nice! I skimmed through the commit and have some questions. (Not sure that I'll be able to re-visit this, though.)

Do you think you could split this up into smaller commits (e.g. one for [IntoIterator] corrections, basically along the lines of your (possibly refinable) bullet list)? I know it puts more burden on your shoulders, but the constant context switching seems to make review quite tedious.

[phimuemue]

Links to Combinations::next (not Iterator::next). Is this canonical?

[tranzystorekk]

I'm not sure, my first thought was that it should point to the itertools documentation instead of sending to the general trait method.

[tranzystorekk]

Do you think you could split this up into smaller commits

Sure, shouldn't be a problem 😄

[tranzystorekk]

As requested, I split the change into smaller commits that should be more palatable 😄

[jswrenn]

bors r+

[bors]

Build succeeded:

• bors build finished