Header blocks render non-breaking space entities

[ConnectGrid]

Header blocks are rendering encoded  . Reviewing the code shows it's written differently from how a Paragraph block is handled, for example.

I tried to fix this by subclassing the library and providing my own parseHeader() method, but with everything having a private visibility, this didn't work.

Are you open to pull-requests to fix these issues?

1. Change visibility from private to protected so that the library can be subclassed.
2. Fix the parseHeader() method.