v4.0.0 - update to v1.81 - with tables

Thanks to the effort by @the-goodies , the wrapper has been upgraded to use v1.81 of Dear ImGui. As part of this upgrade, the support for tables was also added. See #138 for details.

Furthermore, @JetSetIlly helped to unify the names and types of various constants, most notably for bitflags. See #141 for details.

Both modifications included breaking changes, so the major version was bumped to v4.