Etabackend

1. backend: improve COINCIDENCE tool
2. backend: support aiohttp>=3.8.0
3. backend: support single-start-multiple-stop clocks
4. backend: revise error message

**NOTE: The behavior of the [COINCIDENCE Tool](https://eta.readthedocs.io/en/latest/actions.html#coincidence) has changed in this version. Update your recipe if you were using it.**

1. update recipes to support headerless file

1. backend: support A033 time tagger from EvenTech (FORMAT_ET_A033)
2. backend: support FORMAT_QT_RAW
3. gui: fix pip install issues since Python 3.8

1. backend: introducing the new Task API
2. backend: Allow opening the file using memory mapping (mmap), by default off.
3. toolkit: Fixes Simulate growth
4. toolkit: Enable clipping of file in the initial evaluation in the toolkit.
5. toolkit: Fixes an error in the live option to plot using bokeh.
6. testing: add Python 3.9 support
7. gui: added animated eta logo
8. gui: Reload the cached GUI everytime, to avoid being stuck on older GUI versions in electron

This release coincides with the publication of our paper [Z. Lin et al (2021 JINST 16 T08016)](https://doi.org/10.1088/1748-0221/16/08/T08016) describing the ideas behind ETA.

1. gui: fixed updater logic for electron >5.0.0, add static and animated svgs for logo
2. backend: New Action `histogram.clear()`
3. packaging: Updated conda environment yaml file to install everything with conda from the default channels and use pip for etabackend.
4. backend: Enable clipping of file in the initial evaluation in the toolkit.

1. recipes: fixed some problems in qutag lifetime recipe