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.
Remove more warnings.

Mostly of the 'unused imports' kind.
Fix many warnings.
Add a few 'function's.

This is now 100% consistent. Whoops!
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.
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Remove outdated function transmute_for_stage0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.
Remove legacy_modes
Remove two warnings about unneccesary safe blocks.

Since a snapshot was done last night, these are good to go.
auto merge of #6643 : sanxiyn/rust/legacy-modes, r=bstrie
auto merge of #6644 : steveklabnik/rust/remove_unsafe_warning, r=bstrie

Since a snapshot was done last night, these are good to go.
refactoring test functions
parser comment
detect unused attrs in one more place, allow parsing to continue for all

changed a bunch of fatal()'s into err()'s, to allow parsing to proceed.
hygiene infrastructure.

- added a hash table to memoize rename and mark operations.
- added rename, mark, and resolve fold fns
getting rid of interner_key! macro
added and rewrote text for 'do' and 'for' loops