Compressed sections (#152)

Compressed sections (#152)

* Add constants, enums and structs for compressed section

* ELFStructs: update comments for new section numbers in Oracle docs

* Make the ELFFile's stream/structs available to all Section instances

This harmonizes the signature of Section constructors. Besides, structs
will be required to read compressed sections.

* ELFFile._read_dwarf_section: use Section.data to read the section

An upcoming change will add compressed sections handling. In this
context, the DWARF must be parsed from the decompressed data, so reading
the ELFFile stream will be wrong.

* Add ELF compressed debug sections handling