Standardize whether lib descriptions end with a period

[jruderman]

http://static.rust-lang.org/doc/master/std/index.html

str: String manipulation
task: Task management.

[huonw]

This applies to function/struct/etc descriptions too.

[flaper87]

Visiting for triage.

There seems to be 1 (os) lib with a trailing dot but many inconsistencies for functions and struct descriptions. I agree this should be applied everywhere. FWIW, I think the dot is not needed

[aturon]

cc me

[frewsxcv]

Visiting for triaging

Still looks pretty inconsistent. Most (if not all) of the descriptions are not sentences, so I would think they should not end in periods

[bluss]

Discussion and resolution of this would happen in "API comment conventions" rust-lang/rfcs#505 I think.

[steveklabnik]

Today, these almost all end with a period, and I plan on doing so as I go through the docs.

/cc @rust-lang/libs, is that acceptable? Or should I not put one?

[aturon]

@steveklabnik Consistency is most important. I personally like periods in this context, even for sentence fragments.

[alexcrichton]

I don't have much of an opinion beyond ensuring we're consistent, whatever's easiest I'm game for :)