Pyheadtail

Changes:
- bug fix for field map calculation in `FrozenGaussianSpaceCharge`
- `FrozenGaussianSpaceCharge` can recompute field map from beam
- new automated adaptive mode for `FrozenGaussianSpaceCharge`
- PIC / self-consistent space charge: same new automated adaptive mode implemented in `SpaceChargePIC_Adaptive25D`

Bugfixes and more flexibility for damper

- feedback: include damping rate 0 treatment
- frozen space charge field map: bug fix of vertical plane

New feature for FrozenGaussianSpaceCharge25D: providing adaptive mode

The fields are automatically recomputed when the beam RMS size changes. This is controlled via sigma_rtol.

Changes:

- Longitudinal RFBucket matching has been upgraded, support of thermal,
q-Gaussian, parabolic and waterbag distributions. Can easily be extended
to new distribution types. Make sure to check out the notebook
https://github.com/PyCOMPLETE/PyHEADTAIL-playground/RFBucket_Matching.ipynb .
- New FieldMap classes for 1D (horizontal), 2D (transverse) or 3D field maps
including the GPU (uses PyPIC).
- New FrozenSpaceCharge25D allows to apply a frozen transverse field map to a
bunch in slice-by-slice manner, where the longitudinal plane is self-consistently
resolved via slicing by using the local line charge density for the field map.
- New PyPIC version significantly speeds up self-consistent PIC space charge
on GPU (cf. message of commit 28e3cc5 for timing details).
- Self-consistent PIC space charge uses double precision by default now.
- 2D PDF integrators revived and restructured.
- RFBucket allows proper PS Booster accelerating bucket description now (cf. commits d49c460 and 2355c13).
- Release script includes PyPI publication now.
- Minor documentation improvements.
- Some (relevant) bug fixes.

Hotfix: removing pylab imports from feedback module

Furthermore, this PR extends the release script functionality:
- allow releasing patches from hotfix/* branches
(cf. branching model on wiki)
- draft github release form CLI (via gothub tool)

2 fixes of things spotted by Mario, thanks :)
- update obscure dispersion warning to something understandable
- allow higher order chroma to be provided with `np.array` instances