Elaborate a bit in the Reader docs regarding stream position.

Had a conversation with @cmr in IRC about some places that these
docs were confusing. The functions that advance the stream now say so.

In addition, I think that calling out the similarities to familliar C
functions should help people coming from other languages.
Add a better introduction for the io module.

Let's actually give a top-level description of what's in here, eh?
Fix wording per feedback

Thanks @catamorphism!
Removing some warnings from logging.rs

These imports were not being used.
Remove more warnings.

Mostly of the 'unused imports' kind.
auto merge of #6624 : steveklabnik/rust/io_prelude, r=catamorphism

Let's actually give a top-level description of what's in here, eh?
Fix many warnings.
Add a few 'function's.

This is now 100% consistent. Whoops!
auto merge of #6627 : steveklabnik/rust/remove_warnings, r=thestinger,catamorphism

These imports were not being used.
auto merge of #6621 : steveklabnik/rust/expand_reader_docs, r=thestinger

Had a conversation with @cmr in IRC about some places that these
docs were confusing. The functions that advance the stream now say so.

In addition, I think that calling out the similarities to familliar C
functions should help people coming from other languages.
Register snapshots
auto merge of #6629 : steveklabnik/rust/remove_uvio_warnings, r=catamorphism

Mostly of the 'unused imports' kind.

I'm unsure about the 'no unsafe' bit, but that's what it says...
auto merge of #6632 : steveklabnik/rust/remove_more_warnings, r=thestinger

With this, the build is almost 100% warning free.

One more can be fixed after the next snapshot, and there's one other that I filed an issue about already.
auto merge of #6635 : brson/rust/snapshot, r=brson
Remove outdated function transmute_for_stage0

The function was a workaround for bootstrapping that isn't required
anymore and just degrades hashmap performance, as it doesn't get inlined
cross-crate and turns a no-op into a call.
auto merge of #6640 : dotdash/rust/hash_perf, r=bstrie

The function was a workaround for bootstrapping that isn't required
anymore and just degrades hashmap performance, as it doesn't get inlined
cross-crate and turns a no-op into a call.