Configuration.forceExtendedProfile can't be set to false

[denisk20]

The builder for Configuration doesn't have a method to set forceExtendedProfile to false, it only has a method to set it to true which is pointless since the default values is already true.
https://github.com/jdcasey/markdown4j/blob/master/src/main/java/com/github/rjeschke/txtmark/Configuration.java#L163
I can create a PR if someone reading this is capable of merging and releasing a new version.

[jdcasey]

Note that this is only a fork of the original project. Having said that, I'm willing to review / accept PRs and release new versions of this fork. I'm not clear on whether the original codebase is still active.