Laserchicken

Added:
- build_volume module
- the most relevant functions can be now imported directly from laserchicken
- reading/writing of binary PLY and LAZ files, with optional writing of selected attributes
- utility function to merge point-cloud data
- extra log tasks implemented: point-cloud log entries are introduced upon point-cloud loading, filtering, normalizing, merging and assigning to targets.
- select_polygon now supports multi-polygons and optionally return a mask for the selected points

Changed:
- compute neighborhoods returns generator with neighborhoods instead of nested neighborhoods like it did before (breaking change!)
- Some of the existing modules have been renamed/restructured (breaking changes!):
- `normalization` --> `normalize`
- `feature_extraction` created (functions moved from `feature_extractor/__init__.py`)
- `select` and `spatial_selection` merged into `filter`, with the function `select_polygon` allowing to deal with all the spatial selection functionalities
- format-specific `read_*` and `write_*` modules replaced by `load` and `export`
- Dependency on `laspy` replaced by `pylas` + `lazperf` (easier reading/writing of LAS/LAZ files)

Added
- Features added:
- max_intensity
- min_intensity
- range_intensity
- mean_intensity
- std_intensity
- coeff_var_intensity

Changed
- Features renamed:
- max_norm_z --> min_normalized_height
- min_norm_z --> max_normalized_height
- range_norm_z --> range_normalized_height
- mean_norm_z --> mean_normalized_height
- std_norm_z --> std_normalized_height
- coeff_var_norm_z --> coeff_var_normalized_height
- density_absolute_mean_norm_z --> density_absolute_mean_normalized_height
- entropy_norm_z --> entropy_normalized_height
- kurto_norm_z --> kurto_normalized_height
- skew_norm_z --> median_normalized_height
- var_z --> skew_normalized_height
- perc_1_norm_z --> var_normalized_height
- perc_100_norm_z --> perc_1_normalized_height

Added
- Percentiles 1-100
- Percentiles normalized height 1-100
- Band ratio feature extractor
- Function to list available feature extractors
- Tutorial notebook

Changed
- Echo ratio no longer gives percentage (removed factor 100)

Fixed
- Bug in reading ply file with comments in unexpected format
- Bug in normal vector and slope

Removed

Added
- Normalization module
- General tests that all current and future feature extractors will be checked against.
- Possibility to have a randomly subsampled (fixed) number of neighbors (eg for faster feature calculation)
- Added feature extractors based on normalized height

Changed
- Many feature calculations are done in a vectorized way
- z_entropy feature renamed to entropy_z for consistency
- density_absolute_mean feature renamed to density_absolute_mean_z for consistency
- perc_10 features renamed to perc_10_z for consistency

Fixed
- Corner cases for many feature extractors (e.g. zero points)
- Bug in slope feature calculation
- Bug in fix density absolute mean feature calculation

Removed