Merge Beta 3 release branch into master

Update changes for lite

Remove the comments about iterator validation

As it may be implementation dependent.

Update changelogs for C++ maps

Test redundant varint fields decoding in JS.

Remove the instructions for pbconfig.h

Added release notes for Ruby and JavaScript.

Fine-tune build scripts and better documentation.

Bridge vs2008 hashmaps.

Add compatibility notice for Java.

python changes

Varints are generally encoded in minimum possible length but need to
ensure that any redundancy does not break fields decoder.

Move test for standalone BoolValue to JsonParserTest

"make google/protobuf/stubs/pbconfig.h" was added in hope of addressing
the issue that when you "make protoc" from a freshly checked out
project, pbconfig.h will be reported missing. However, the trick doesn't
seem to work. Instead, add instructions in the document to work the issue
around.

Also document why MSYS2 cannot be used for publishing protoc.

Beta 3

Initial draft for changelog.

Update version numbers for beta3

Fix C++ Boost incompatibility on Windows/MSVC

Also added a standalone formatter test, for confidence.
Have validated that undoing the change in 835fb947 breaks the tests
(i.e. we are still testing that the change is required).

Fix C# Json parsing of well-known type Boolvalue

Fix the command line interface unittest again

This time move the macro inside namespaces; hopefully will work with the
integration script.

Fix protoc build artifact script.

pbconfig.h has gone. This commit removes the target.