Waltlabtools

- Corrected source directory structure

- Added function `dropna` to clean data for uses where only finite
numbers are allowed (e.g., scipy.optimize.curve_fit in
waltlabtools.regress)
- Moved everything from the nonnumeric module into the core module
- Created new modules cal_curve and model for the classes CalCurve and
Model, respectively

- Rearranged modules

- Fixed a bug in read_quanterix

- Renamed read_hdx module to read_quanterix to provide for future
expansion to SP-X and other instrumentation
- Added module docstrings
- Attempted to build conda packages for different versions of conda
- Added read_quanterix.sample_results function

- Removed some type hints and improved documentation