Debuggingbook 1.1

(* We now support (but also require) Python 3.9 or later. Earlier versions still required Python 3.6 due to some outdated modules such as astor and enforce we depended upon (and now don't anymore).

• We made an optimization in DeltaDebugger.dd() to distribute changes more evenly over the input space. This will change dd() results in some cases, but overall improve performance. Thanks to Olad Chitil and Joanna Sharrad for reporting this!
• We fixed two issues in DeltaDebugger.dd(), specifically #45 and #46. Thanks to @TheSilvus for reporting this!
• We added missing dependencies to the debuggingbook pip package (Issue #44) such that pip install debuggingbook also installs all the packages it depends upon. Thanks to @TheSilvus for reporting this!
• We fixed a warning '.gitignore is a symbolic link' during git checkout (Issue #43) Thanks to @rjc for reporting this!