E57

- Fixed typo in `intensityMaximum` XML tag when writing E57 files.
- Added missing support for non-integer color and intensity limits when writing E57 files.

- Breaking Change: Fixed typo in public API to register E57 extensions.
- Fixed reading E57 files without data3D or images2D tags in XML section.
- Added public API to write and read arbitrary blobs for E57 extensions.
- Added public API to allow XML customization for E57 extensions.
- Extended documentation and example code for E57 extensions.
- New flag for e57-unpack tool to extract only images and skip point data (thx Graham!)

- Fixed handling of integer values when min and max values are equal.
- Very minor documentation improvements.
- Enabled and fixed additional Clippy lints.
- Deleted some unused code from paged reader.

- Smaller perfomance improvements for reading E57 files.
- Fixed paged writer boundary crossing errors (thx nil-vr!)
- Fixed alignment issues after writing image blob sections (thx nil-vr!)

- Updated `roxmltree` dependency to 0.19, which removes the indirect dependency to `xmlparser`.
- Fixed handling of integers and scaled integer values without explicit min and max values.
- Fixed handling of big integer and scaled integer values (avoid i64 overflows).
- Allow bigger integer ranges in the simpler iterator for invalid state values.
- Make simple iterator more robust against weird color and intensity values.
It will now use zero values as fall back in case a value cannot be mapped to a unit float.

- Fixed bug when converting Cartesian to spherical coordinates.
The code used `atan2(x, y)` instead of `atan2(y, x)` which flipped the data horizontally.
This problem was not detected since the unit tests were too simple.
They have now been extended to capture this issue.