Legwork

*TW 18/11/21*
- Add a factor of 10/3 to the TianQin sensitivity curve to make it consistent with LISA (thanks to Yi-Ming Hu for pointing this out!)

*KB 18/11/21*
- Make confusion noise follow shape of supplied frequency even in case of no confusion

*TW 17/11/21*
- Add `custom_psd` to the `sc_params` in `Source`
- Change the default parameters of `Source.get_snr()` to use `sc_params`

*TW 16/11/21*
- Move `determine_stationarity` from `utils` to `evol` to avoid cyclical imports

*TW 12/11/21*
- Change default values for `small_e_tol` and `large_e_tol` in `get_t_merge_ecc`
- allow users to specify custom confusion noise in sensitivity curves

*TW, 5/11/21*
Small changes to visualisation code and updates to tutorials/demos with the new code
- allow user to specify weights in `Source` and visualisation functions
- allow user to customise sensitivity curve in any use of `plot_sources_on_sc`
- `legwork.__version__` now prints the version number
- Add new demo about verification binaries and other miscellaneous docs fixes