Update readelf to v2.37, adapt readelf.py output and tests (#387)

Update readelf to v2.37, adapt readelf.py output and tests (#387)

Changes to conform the output of readelf.py to binutils readelf v2.37:

- Use singular "entry" when needed instead of "entries".

- Output the last entry for the .debug_line output table when
  DW_LNE_end_sequence is encountered, as DWARF standard dictates. Looks
  looks like this was a readelf bug which was fixed in commit
  ba8826a82a29a19b78c18ce4f44fe313de279af7 of the GNU binutils-gdb repo.

- Add additional "Stmt" field in the .debug_line output table, and
  ignore the new "View" field. The "Stmt" field has been implemented in
  readelf.py. The "View" field is not something that the DWARF standard
  defines, it's an internal register added to the line number
  information state machine by binutils to perform assembler checks (see
  commit ba8826a82a29a19b78c18ce4f44fe313de279af7 of GNU binutils-gdb
  repo for more info, in particular gas/doc/as.texinfo). "View" is
  unimplemented in pyelftools for now and a special case has been added
  in the readelf test suite to ignore it.

- Add support for printing section names when dumping .symtab entries of
  st_type STT_SECTION as readelf v2.37 does (see commit
  23356397449a8aa65afead0a895a20be53b3c6b0 of GNU binutils-gdb repo).

- Add suport for recognizing SOs specifically tagged as PIE (DT_FLAGS_1
  dynamic tag with DF_1_PIE set). In such case, describe the file as
  "Position-Independent Executable file" instead of "Shared object
  file", as readelf v2.37 does.

- Add leading "0x" for version section addresses when dumping version
   information (-V) as readelf does.

- Ignore "D (mbind)" in section headers flags legend (pyelftools does
  not output this flag).

Special cases ADDED for run_readelf_tests.py:

- Ignore "View" column for --debug-dump=decodedline in readelf's output.
- Ignore ellipsis ("[...]") for long names/symbols/paths in readelf's
  output.

Special cases REMOVED for run_readelf_tests.py:

- Detection of additional '@' after symbol names (flag_after_symtable)
  seems to no longer be needed as all tests pass whitout this exception.
- Special case for DW_AT_apple_xxx seems to no longer be needed, readelf
  now recognizes those.
- Special case for PT_GNU_PROPERTY no longer needed, readelf now
  recognizes it.

Other changes:

- Add missing import in elftools/dwarf/lineprogram.py.

References:

- GNU binutils-gdb repo: https://sourceware.org/git/?p=binutils-gdb.git