Fluidimage

- New topologies and executors with Trio!
- Much better coverage & many bugfixes!
- Better surface tracking

- Requirement Python >= 3.6
- Surface tracking
- image2image preprocessing
- BOS topology
- Handle .cine file
- Calibration
- fluidimslideshow-pg and fluidimviewer-pg (based on PyQtgraph)
- OpenCV backend for preprocessing

- Bug fixes and documentation changes.
- Continuous integration (python 2.7 and 3.5) with bitbucket pipelines
([coverage ~40%](https://codecov.io/gh/fluiddyn/fluidimage))
- Preprocessing of images.
- First simple GUI (`fluidimviewer` and `fluidimlauncher`).

- Topology and waiting queues classes to run work in parallel.
- PIV work and topology (multipass, different correlation methods).