Biopeaks

+ enhancement: added support for [EDF files](https://en.wikipedia.org/wiki/European_Data_Format).
+ enhancement: `ecg.ecg_peaks()` now filters out power-line noise at 50Hz. This
further increases the performance on the [Glasgow University Database (GUDB)](http://researchdata.gla.ac.uk/716/).
Again, the GUBD has not been used to optimize `ecg.ecg_peaks()` in any way prior to
the performance evaluation. The tolerance for peak detection was set to one
sample.

|condition|metric |summary|version 1.0.2|version 1.0.3|version 1.1.5
|:-------:|:---------:|:-----:|:-----------:|:-----------:|:-----------:
|sitting |precision |mean |.999 |.998 |.998
| | |std |.002 |.005 |.002
| |sensitivity|mean |.996 |.996 |.998
| | |std |.008 |.004 |.004
|handbike |precision |mean |.904 |.930 |.984
| | |std |.135 |.127 |.022
| |sensitivity|mean |.789 |.857 |.984
| | |std |.281 |.247 |.025

+ enhancement: improved ECG artifact detection and correction.

+ bugfix: `controller.edit_peaks()` works properly again.
+ enhancement: moved the modality menu to processing options.

+ enhancement: improved sensitivity of `ecg.ecg_peaks()` without decreasing
precision in moderately dynamic conditions (handbike) while maintaining
high performance in resting conditions (sitting). Performance has been
evaluated on lead 2 of all 25 subjects in the [Glasgow University Database (GUDB)](http://researchdata.gla.ac.uk/716/).
The GUBD has not been used to optimize `ecg.ecg_peaks()` in any way prior to
the performance evaluation. The tolerance for peak detection was set to one
sample.

|condition|metric |summary|version 1.0.2|version 1.0.3
|:-------:|:---------:|:-----:|:-----------:|:-----------:
|sitting |precision |mean |.999 |.998
| | |std |.002 |.005
| |sensitivity|mean |.996 |.996
| | |std |.008 |.004
|handbike |precision |mean |.904 |.930
| | |std |.135 |.127
| |sensitivity|mean |.789 |.857
| | |std |.281 |.247

+ enhancement: `resp.resp_extrema()` is now based on zerocrossings and makes
fewer assumptions about breathing rate.

+ bugfix: `controller.save_signal()` now preserves the header if the data are
saved to the same location (i.e., if `model.rpathsignal` and `model.wpathsignal` are
identical).