Fix: Corrected issue #233 with struct.pack()

[thats-i-t]

• Fix: Corrected issue Issue with SxI.header_format = 'HEADER_LEN_BYTE' #233 with struct.pack() by previous check of struct.size
• Added artefacts from installing package in editable mode to .gitignore

Types of changes

• [ x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• [ x ] I have read the CONTRIBUTING document.
• [ x ] My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• [ x ] All new and existing tests passed.