HeaderDoc support in the library and generated sources

- Convert most of the core library headers over to HeaderDoc format.
- Switch the generated comments over to HeaderDoc.
- Create GPBCodedOutputStream_PackagePrivate and move some things into there
  that should be more internal.
diff --git a/objectivec/GPBCodedOutputStream.m b/objectivec/GPBCodedOutputStream.m
index 70142e6..fd9ed66 100644
--- a/objectivec/GPBCodedOutputStream.m
+++ b/objectivec/GPBCodedOutputStream.m
@@ -28,7 +28,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#import "GPBCodedOutputStream.h"
+#import "GPBCodedOutputStream_PackagePrivate.h"
 
 #import <mach/vm_param.h>
 
@@ -178,12 +178,6 @@
   return [self initWithOutputStream:nil data:data];
 }
 
-- (instancetype)initWithOutputStream:(NSOutputStream *)output
-                          bufferSize:(size_t)bufferSize {
-  NSMutableData *data = [NSMutableData dataWithLength:bufferSize];
-  return [self initWithOutputStream:output data:data];
-}
-
 // This initializer isn't exposed, but it is the designated initializer.
 // Setting OutputStream and NSData is to control the buffering behavior/size
 // of the work, but that is more obvious via the bufferSize: version.
@@ -199,15 +193,10 @@
   return self;
 }
 
-+ (instancetype)streamWithOutputStream:(NSOutputStream *)output
-                            bufferSize:(size_t)bufferSize {
-  return [[[self alloc] initWithOutputStream:output
-                                  bufferSize:bufferSize] autorelease];
-}
-
 + (instancetype)streamWithOutputStream:(NSOutputStream *)output {
+  NSMutableData *data = [NSMutableData dataWithLength:PAGE_SIZE];
   return [[[self alloc] initWithOutputStream:output
-                                  bufferSize:PAGE_SIZE] autorelease];
+                                        data:data] autorelease];
 }
 
 + (instancetype)streamWithData:(NSMutableData *)data {