protobuf: updated to 3.11.0

Protocol Buffers v3.11.0

C++
Make serialization method naming consistent
Make proto runtime + generated code free of deprecation warnings
Moved ShutdownProtobufLibrary() to message_lite.h. For backward compatibility a declaration is still available in stubs/common.h, but users should prefer message_lite.h
Removed non-namespace macro EXPECT_OK()
Removed mathlimits.h from stubs in favor of using std::numeric_limits from C++11
Fixed bug in parser when ending on a group tag
Add a helper function to UnknownFieldSet to deal with the changing return value of message::unknown_fields()
Fix incorrect use of string_view iterators
Support direct pickling of nested messages
Skip extension tag validation for MessageSet if unknown dependencies are allowed
Updated deprecation macros to annotate deprecated code
Remove conversion warning in MapEntryFuncs::ByteSizeLong
Revert "Make shared libraries be able to link to MSVC static runtime libraries, so that VC runtime is not required."

Python
Add float_precision option in json format printer
Optionally print bytes fields as messages in unknown fields, if possible
FieldPath: fix testing IsSet on root path ''
Experimental code gen (fast import protobuf module) which only work with cpp generated code linked in


(adam)