Add BuilderOption: keepEntityCharRefs

[jasonkhanlar]

Please include a summary of the change and which issue is fixed. Fixes # I have no idea if this fixes anything other than my own personal fix that seems to be sufficient for my use case, and I thought I'd share in case anyone may want to consider creating their own code to reproduce this or whatever. You can even reject this pull request as it is not intended to be of any value or use otherwise even if it is of value or use, because anyone and everyone can probably figure out this themselves without me contributing such code, however, since nobody seems to have done so, I tried to make sense of something (or at least I think I did, but I don't even know what I'm doing so I have no idea if this even makes sense)

keepEntityCharRefs:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Notes (delete after reading):

• Please make sure this change is thoroughly tested. Add your tests to the test folder in a relevant sub folder. If this pull request is a bug fix, add a test specific to the fixed issue in the test/issues sub folder. If this change decreases code coverage you may be asked to add additional tests.

I have no idea how to thoroughly test anything, but I did write lots of English language words here: #117