Issue #20786: Fix signatures for dict.__delitem__ and property.__delete__
Issue #20568: Fix typo in pip option.
 Issue #20748: Uninstalling pip does not leave behind the pyc of
 the uninstaller anymore.
Issue #20465: Update Windows installer to SQLite 3.8.3.1.
Issue #14512: Launch pydoc -b instead of pydocgui.pyw on Windows.
whatsnew: add some issue number annotations.

Add issue number to tick_counter, PyOS_ReadlineFunctionPointer, marshal
optimizations (add Antoine's contribution to the entry under the marshal
module), and absolute paths in __file__.