Pytransform3d

**Bugfix (Breaking Change)**

* Fixes extrinsic zxz and zyz Euler angles (order of rotations was previously inverted)

**Features**

* Adds functions `vector_projection` and `check_skew_symmetric_matrix`
* Adds screw parameters, screw axis, exponential coordinates of transformations, screw matrix, and matrix logarithm as new representations for transformations
* Adds function `adjoint_from_transformation`
* Adds method `TransformManager.remove_transform`
* Adds functions `norm_matrix` and `matrix_from_two_vectors`

**Documentation**

* Rearranges gallery in readme
* Links to GitHub page in sphinx documentation
* Improves documentation of SE(3)
* Adds examples to documentation with sphinx-gallery and a custom image scraper for Open3D
* Documents rotation and transformation conventions of other software packages

* Adds major improvement of pytransform3d's visualization and animation capabilities: a renderer based on Open3D's visualizer which is fast and easily accessible. In addition to meshes it can also easily render large point clouds etc. The interface that is exposed by pytransform3d is similar to matplotlib.
* Adds `axis_angle_from_two_directions`
* Adds support for prismatic and continuous URDF joints
* Adds support for material tag in URDF parser
* Adds option to turn checks in TransformManager off to make it faster

**Rotations**
* Introduces *compact axis-angle* as a new concept to represent orientations and adds conversions from and to axis-angle, quaternion, and rotation matrix
* Uses compact axis-angle to represent angular velocities
* Adds function to compute time derivatives of a quaternion sequence
* Adds function to integrate angular velocities to a sequence of quaternions
* Adds additional functions to convert Tait-Bryan or Euler angles to rotation matrices

**Transformations**
* Adds vector_to_direction, vectors_to_directions, and vectors_to_points

**Documentation**
* Less confusing documentation of active, passive, extrinsic, and intrinsic rotation conventions
* Documents how multiple transformations should be modeled

**Plotting**
* Adds plotting functions for geometric objects
* Extends plotting function for cylinders to include cylindrical shells
* Plots convex hull of meshes by default when plotting URDFs to speed up visualization
* Passes option 'prog' to pydot
* Adds function plot_vector

Adapt to change in Matplotlib interface

* Update check mechanisms
* Check determinant of rotation matrices
* Increase tolerance of checks for rotation matrices
* Allow deactivation of ValueErrors for invalid rotation and transformation matrices with argument `strict_check=False` in several functions and in the `TransformManager`
* Bugfixes
* Improve numerical stability of `axis_angle_from_matrix(...)`
* Improve numerical stability of `angle_between_vectors(...)`
* Fix SLERP between identical orientations
* It is now possible to plot visual / collision meshes of a URDF (with trimesh)
* Improved documentation of conventions for axis-angle representation

Minor fixes and additional functions:

* Compatibility to newer sphinx versions
* Compatibility to matplotlib >= 3.1
* Fix orientation of frame annotation
* Pass kwargs in plot_trajectory
* Add TransformManager.has_frame and TransformManager.connected_components