Makeelf

Features:
- append_symbol now returns index of new symbol

Bugfixes:
- improper usage of is operator

Others:
- new tests
- documentation updates
- development of new CI workflow

Fixes:
- endianness issues during creation of ELF object (5, 6)
- missing imports (5)

Fixes:
* Version number in setup.py

Changes:
* Elf32_Sym and related enums (STB, STT, STV) are moved to elfsect
* Implemented Elf32_Dyn for .dynamic section manipulations
* sections on Elf.sections can now be list of serializable objects (e.g. Elf32_Dyn)

Fixes:
* little-endian ELFs were not read properly
* if sh_type contained unknown value, it was not possible to deserialize object
* sh_type used wrong endianness
* minor fixes

Fixes in setup.py

Changed project structure. First release, uploaded to PyPI