Pydynamic

Fix
* **DFT_deconv:** Replace the imaginary part of H by Y's imaginary part in one of the equations ([`a4252dd`](https://github.com/PTB-M4D/PyDynamic/commit/a4252ddd850908467933d7de41f1da99d57d3ea1))

Documentation
* Introduce Python 3.9 to the docs and actually provide requirements*.txt files ([`19dcef2`](https://github.com/PTB-M4D/PyDynamic/commit/19dcef2f5b1d0516dc9ebf462d5115a5554c8cec))

Feature
* **interp1d_unc:** Add cubic bspline interpolation-kind ([`f0c6d19`](https://github.com/PTB-PSt1/PyDynamic/commit/f0c6d19bad71816f5c6d95803f734e77567931ea))

Documentation
* **interp1d_unc:** Add example for kind = "cubic" ([`8c2ce38`](https://github.com/PTB-PSt1/PyDynamic/commit/8c2ce38af4cb4a391da9e82c23c5754f494892ad))

Feature
* **propagate_convolution:** Convolution with full covariance propagation ([`299165e`](https://github.com/PTB-PSt1/PyDynamic/commit/299165ef630ef54bcb877e8a3260038805609e4f))

Documentation
* **propagate_convolution:** Add module description ([`ffafa00`](https://github.com/PTB-PSt1/PyDynamic/commit/ffafa00ea8961bdd4e4414645102f6870063f3d7))
* **DFT_deconv:** Improve wording of docstring for return value ([`e866aa4`](https://github.com/PTB-PSt1/PyDynamic/commit/e866aa41212767f9b24f966bfabf005c9f6cdf39))

Feature
* **FIRuncFilter:** Add FIR filter with full covariance support ([`b937a8b`](https://github.com/PTB-PSt1/PyDynamic/commit/b937a8b979f947df3149aeda38401b90fc522ef4))

Documentation
* **trimOrPad:** Enhance docstring ([`4c0da58`](https://github.com/PTB-PSt1/PyDynamic/commit/4c0da58e2c9d2bcae212a757f7b80ef65f602cd1))
* **_fir_filter:** Adjust docstring and ValueError ([`090b8f8`](https://github.com/PTB-PSt1/PyDynamic/commit/090b8f832c54e4cb969de70d5825d5000410eacc))

Fix
* Flip theta in uncertainty formulas of FIRuncFilter ([`dd04eea`](https://github.com/PTB-PSt1/PyDynamic/commit/dd04eeace70ce4fe7a81fb432cc117f80af74d4f))