E57

- Fixed two bugs that prevented intensity limits from being read correctly.
- Made color and intensity normalization optional (still enabled by default).
- Better intensity and color normalization using the proper limits of the point cloud.
The library was using the type ranges before, which is now only a fallback.
- Allow setting intensity and color limits manually when writing point clouds.
- Improved documentation related to color and intensity topics.

- Fixed reader bug that occured for some cases when a point cloud contained values where min=max.
See issue 12 for more details: https://github.com/cry-inc/e57/issues/12
- Added some convenience helpers for getting Cartesian bounds.
- Some very minor documentation improvements.

- Fixed critical writer bug that occurred when the compressed vector
section header and the data offset were not in the same page.
In such cases the the data offset was off by the 4 bytes,
(which is the size of the CRC32 checksum).
- Fixed potential alignment bug in writer when doing early outs while writings points to disk.
- Updated example code to use the latest version of the LAS crate.

- Fixed critical writer bug that could produce invalid E57 files.
This occured when point attributes sizes were not full bytes,
for example intensity integer values between 0 and 2047.
In other cases the file was valid, but contained wrong values for such attributes.
- Fixed minor corner case in reader when a data packet did not contain a full point.

- **This version was yanked from crates.io and is no longer available!**
- Broken fix for critical writer bug that could produce corrupt E57 files.

- Updated `roxmltree` dependency to version 0.20.