Currently, when configuring with --disable-shared the following error is
generated when running make check:
make[2]: *** No rule to make target `../lib/.libs/*.o',
needed by `main'.  Stop.
make[2]: *** Waiting for unfinished jobs....

This commit adds a conditional for this case.

extend callback is only called when server sends MAX_STREAMS frame.
The initial limit must be set explicitly.

Add struct tags for structs used in callbacks.

This allows them to be forward declared. Typedefed anonymous structs
cannot be forward declared without a tag.

Remove final newlines from log messages.

Adding the final newline is left to the logging implementation.