Implement BigInt and BigUint.
Move BigUint and BigDIgit to std::bigint.
Convert std::bigint to explicit self.
Impl Zero, One of BigInt, BigUint
Convert @[BigDigit] to ~[BigDigit]
Enhance auto_encode to take number of struct fields

emit_struct and read_struct takes an additional len:uint parameter which tells
us how many fields the struct we are working on has.

This is required to implement an Encoder for the msgpack [1] serialization
format. To serialize a struct with msgpack you have to use arrays and the size
of the array has to be know before each of the elements are written out. JSON
as an example doesn't have this problem as it uses '[' and ']' delimiters for
arrays.

[1]: www.msgpack.org
Fix two minor issues in the tutorial.

Remove an extraneous 'then', and replace 'second' with 'first'.
Add option::get_zero

r=brson

Closes #3797
core: fix windows breakage, r=burningtree.
Make either::{partition, flip, to_result} take their arguments by-value

Addresses an XXX

r=pcwalton
Rename option::get_default => get_or_default, get_zero => get_or_zero
Merge remote-tracking branch 'superoptimizer/master' into HEAD

Conflicts:
	doc/tutorial.md
Add Mark Lacey to AUTHORS
librustc: Stop generating first-class aggregates in visit glue, since they kick us off fast isel. Closes #4352. rs=minor-perf-improvement
Trivial cleanup: use enum_is_univariant; no functional change intended.
Make consts of degenerate nullary enums not ICE.

This makes the const construction code match the logic in type_of.
Add a test for nullary univariant enums.
rt: Stop zeroing out all allocations. Unobservable perf win. Closes #2682. rs=negligible-perf-win
librustc: Fix unconditional ty_to_str call in ty.rs. Was heaviest path in allocation. Negligible perf win. rs=perf-fix
librustc: Remove some string allocations. rs=perf