Migrate writer to printer for C#

Add cmake support.

Change-Id: I121cb70bfdc4894c297ab1a36f1db47736c0652b

Remove Android.mk

Add protoc path detection for Mac OS

This file bares a different copyright license and also doesn't actually
work (out-dated file lists, no config.h/pbconfig.h, refers to inexist
AOSP paths).

Fix two issues on vs2010.

Add remaining not-already-imported well known types files to podspec

Fix unittest in i386

Document why the podspec is on the root of the repo

A few corrections to the proposed podspec

Change the C# enum generator inherit from primitive generator

RepeatedField::begin()/end() will return NULL when the content is empty.
Passing these NULL values to std::copy() will result in runtime complains
from some compilers (e.g., vs2010).

destroy() should always call the destructor because the caller may rely on
the destructor to do clean-ups.

Add oneof support for c#

default configuration. In default configuration, maven needs webdav for
deployment, which cannot be found in central repository.

Make MapAllocator work with C++11.

Change-Id: I0e1d9e248403631cb57ebed5231e85d19b9bb3df