Specifically:
- introduced notion of "underlying type"
- removed notion of type compatibility
- consolidated rules about assignment compatibility in
  assignment compatibility section
- be consistent with specyfing that nil is the value
  for uninitialized variables that can be nil (this
  was not specified clearly for pointers, functions, interfaces)
- added/fixed various related links throughout
- clarify language on conversions

R=rsc, r, iant, ken2
CC=golang-dev
https://golang.org/cl/1536041

R=rsc
CC=golang-dev
https://golang.org/cl/1514041

R=r
CC=golang-dev
https://golang.org/cl/1535041

R=r
CC=golang-dev
https://golang.org/cl/1539042

R=rsc, iant
CC=golang-dev
https://golang.org/cl/1567041

R=rsc
CC=golang-dev
https://golang.org/cl/1559041

R=gri
CC=golang-dev
https://golang.org/cl/1548042

Time (us) to draw a 200x200 src onto an image.RGBA dst with the Over
operator. Each case was measured three separate times, and the sorted
times are reported.

Fill case (where src is an image.ColorImage):
Before:
7438, 7511, 7526
After:
3073, 3087, 3102

Copy case (where src is an image.RGBA):
Before:
9506, 9510, 9563
After:
5262, 5300, 5344

R=rsc
CC=golang-dev
https://golang.org/cl/1532041

R=rsc
CC=golang-dev
https://golang.org/cl/1533041

R=rsc
CC=golang-dev
https://golang.org/cl/1518042

Specifically:
- Simplified definition of comparison compatibility and folded into
  section on comparison operators since it's only used there.

This is a small language change/cleanup. As a consequence:
- An interface value may now be compared against a non-interface value.
- Channels with opposite directions cannot be compared directly anymore
  (per discussion with rsc).

R=rsc, r, iant, ken2
CC=golang-dev
https://golang.org/cl/1462041

R=r
CC=golang-dev
https://golang.org/cl/1472042

R=rsc, r
CC=golang-dev
https://golang.org/cl/972046

  - cannot send body
  - should not send body-related headers

R=r
CC=golang-dev
https://golang.org/cl/1499041

Also fix an interface bug: white-space-delimited doesn't work well for cases like "%d, %d" on "23, 23")

R=rsc
CC=golang-dev
https://golang.org/cl/1502041

Was timing Exp, not Exp2.

R=rsc, r
CC=golang-dev
https://golang.org/cl/1521042

R=r
CC=golang-dev
https://golang.org/cl/1473042

R=rsc
CC=golang-dev
https://golang.org/cl/1522041

R=rsc
CC=golang-dev
https://golang.org/cl/1503041

    charclass to avoid unnecessarily iterating over ranges.
    Also, use the fact that IntVector is an []int to avoid method calls.
    On my machine, this brings us from ~27500 ns/op to ~17500 ns/op in the benchmark I've added (it is also faster in the case where a range check
    doesn't help, added a benchmark for this too.)

    I'd also like to propose that "[]", and "[^]" be disallowed. They aren't useful as far as I can tell, they aren't widely supported, and they make reasoning about character classes a bit more complicated.

R=r
CC=golang-dev
https://golang.org/cl/1495041

Also added more tests for acosh, hypot, log, log10, log2
in all_test.go.

R=rsc
CC=golang-dev
https://golang.org/cl/1417041

R=rsc, r
CC=golang-dev
https://golang.org/cl/1238044

R=rsc
CC=golang-dev
https://golang.org/cl/1486041

On error, ReadSlice is defined to return the available data
and advance past that data, but it was not behaving that
way for err == ErrBufferFull, making it harder for callers to
handle well.

R=r
CC=golang-dev
https://golang.org/cl/1480041

- provide convenience functions for scanning strings
- enable Scanf etc.
- update doc comments

R=rsc
CC=golang-dev
https://golang.org/cl/1451044

R=gri
CC=golang-dev
https://golang.org/cl/1372042

R=r, iant
CC=golang-dev
https://golang.org/cl/1433042

R=rsc, r, iant
CC=golang-dev
https://golang.org/cl/1465041

R=rsc
CC=golang-dev
https://golang.org/cl/1475041

- implement scanning for all renamed types
	(compiler bug stops complex from being renamable,
	so it can't be tested but the code is there)
- %q %x for strings
- error handling now done with panic/recover

R=rsc
CC=golang-dev
https://golang.org/cl/1458041

- implement scanning for all renamed types
	(compiler bug stops complex from being renamable,
	so it can't be tested but the code is there)
- %q %x for strings
- error handling now done with panic/recover

R=rsc
CC=golang-dev
https://golang.org/cl/1458041

R=ken2
CC=golang-dev
https://golang.org/cl/1442042

Fixes #820.

R=rsc
CC=golang-dev
https://golang.org/cl/1453041

R=rsc
CC=golang-dev
https://golang.org/cl/1395041

R=rsc
CC=golang-dev
https://golang.org/cl/1258044

  For example, earlier, the regexp would accept SIGQUEUE_MAX
  as a unix signal with name SIGQUEUE. Now it is ignored.

R=iant
CC=golang-dev, golang-nuts, joel.sherrill
https://golang.org/cl/1452041

R=adg
CC=golang-dev
https://golang.org/cl/1454041

R=rsc
CC=golang-dev
https://golang.org/cl/1444041

R=golang-dev, adg
CC=golang-dev, rsc
https://golang.org/cl/1426042

"change the encoding of uints...".

R=r
CC=golang-dev
https://golang.org/cl/1436041