Release libdwarf 0.7.0

About 50 vulnerabilities (found by fuzzing) reading corrupt DWARF and/or Elf have been fixed.

Support for 32 bit section numbers (standard Elf has 16 bit section numbers) means
that users calling dwarf_object_init_b()/dwarf_object_finish()
have a source incompatibility to deal with.

Two functions reading the .debug_names section
dwarf_dnames_abbrev_by_code()
and dwarf_dnames_abbrev_form_by_index() were hard to
use and/or broken. They are not needed so they have
been removed.