Header declaration.
LogWriter::writeHeader() refactoring.

fileDescriptorSet -> header.
v1::MessageType implementation.
v1::MessageTypePool implementation.
v1::LogWriter implementation.
LogWriter refactoring.

MessageTypePool parent was replaced by messageTypePool() member.
LogReader refactoring.

MessageTypePool parent was replaced by messageTypePool() member.
v1::LogWriter style fix.
v1::MessageTypePool::Init() bug fix.
v1::MessageTypePool::type() fix.

Invalid id is treated as error.
v1::LogReader implementation.
openReadOnly() and openWriteOnly() implementation.