Drop vs build stuff for inspector

Now that the inspector sources are built as part of gtk/, this should
no longer be needed.
Cosmetic fixes
Use subdir-objects for docs/tools
Add missing docs

Document GtkSwitch::state_set.
Cosmetic formatting fixes
Generate README and INSTALL from configure
Drop an unused function
Quiet a rule
Fix ChangeLog generation

missing is no longer in the toplevel directory.
Also, clean up some file lists.
Fix distcheck

Using an absolute path with subdir-objects failed in distcheck.