* uses namespaces for nested messages and enums
* fixes namespaces for PHP dist
* fixes namespace for Descriptors, adds Cardinality and Kind
* fixes nested namespaces for reserved words and adds tests
* adds tests and generator fix for php class prefixes
* fixes escaping of protobuf packages, enum comments, misc others
* nice refactor of generated code
* adds class files for backwards compatibility
* simplifies code with templates
* adds compatibility files to makefile
* cleanup of generator and fixes nested namespace bug
* regenerates proto types
* remove internal BC classes
* adds deprecated warning, adds methods back
* simplifies if statement
* fixes dist files
* addresses review comments
* adds back TYPE_URL_PREFIX constant
* adds @deprecated to old nested class files
* skips tests which require a separate process when protobuf.so is enabled
* Adds tests for legacy nested classes that do not require separate processes to test
* uses legacy names for GPBUtil message check
* adds block for IDE @deprecated message
* Namespace for nested message/enum in c extension
* Remove unused code
