After loading, the data model in memory should resemble the original ELF file as closely as possible,
so that ELF viewers based on elfio will print out the original values, not the calculated ones.

Fix the following MSVC compiler warning:

elfio/elfio_note.hpp(77): warning C4267: 'initializing' : conversion from 'size_t' to 'ELFIO::Elf_Word', possible loss of data

by changing the type of max_name_sizei to Elf_Xword, as
note_secton->get_size() returns Elf_Xword and note_start_positions also
contains members of type Elf_Xword.

Don't cast away const qualifiers when accessing const data (e.g. section
data). This fixes the warnings such as the following when compiling with
GCC and the -Wcast-qual flag set:

warning: cast from type ‘const char*’ to type ‘ELFIO::Elf_Word* {aka unsigned int*}’ casts away qualifiers [-Wcast-qual]

There are discrepancies in documentations. SCO documentation
(http://www.sco.com/developers/gabi/latest/ch5.pheader.html#note_section)
requires 8 byte entries alignment for 64-bit ELF file,
but Oracle's definition uses the same structure
for 32-bit and 64-bit formats.
(https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter6-18048.html)

It looks like EM_X86_64 Linux implementation is similar to Oracle's
definition. Therefore, the same alignment works for both formats

Previously, when assigning 'name' as a string, it's length was specified
using the full length of 'namesz'. However, this length includes the
trailing '\0' of the underlying char[]. This ultimately causes the C++
string that is created to (incorrectly) contain the '\0' character as
well. This leads to problems where e.g. the following will return false,
even when 'name' itself actually contains the string "GNU\0":

  if (name == "GNU") {
    return true;
  }
  return false;

To fix this, we should only include the length of the string minus the
trailing '\0'.

This change makes it possible to use the regular API to build up
elf files which include the file header.