Becquerel

Major:
* Define bins (integers) and bin_edges_raw while deprecating the use of channels since this was misleading when handling listmode data with large ADC bit depth (i.e. `2**16`). (187)
* Update `Spectrum` `bin_width` and `bin_center` properties for raw and kev values.
* Add listmode data compatibility with `Spectrum` (183)
* Change energy calibrations to use channels instead of bins (184)

Minor:
* Update `PeakFinder` to follow bin vs channel standard defined above. This still requires refactoring to comply fully.
* Add `Spectrum` bin query methods
* Fix min version of uncertainties package (190)
* Note issues with physics.nist.gov. Closed without resolution since connection issues stopped. (185)
* Fix edge case in SPE file parser with files from gadras. (186)

* Make parsing of NIST element data more robust
* NIST element data parsing errors with different Pandas versions
* Changed two plots to plot cps instead of counts
* Fix NIST element and material data parsers
* NIST material data errors
* Updated README with pip install. Improved developer instructions
* Small fixes in spectrum_file
* Parser warning for calibration

Hotfix for the following:

- Resolves issue with installing from PyPi in `python2`
- Adds `MANIFEST.in` for non-source text files
- Updates `RELEASING.md` for tagging, testing and uploading instructions
- Bumps MICRO version

* New feature: Spectrum plotting
* New feature: Spectrum rebinning
* New feature: Spectrum autocalibration tools
* Miscellaneous Spectrum bug fixes and enhancements
* Fix Spectrum multiplication, addition and subtraction problems
* Allow Spectrum counts calculation from cps and livetime
* Allow negative inputs to Spectrum
* Added more example Spectrum files
* Fixed SPE file parser warnings
* Reduced CNF and SPC parser verbosity
* Renamed example notebooks
* Added energy calibration example notebook
* Added overview notebook
* Improved test fixtures
* NNDC query bug fixes
* Cleaned up package import structure
* Cleaned up dependencies
* Added CONTRIBUTING and RELEASING instructions
* Staged package for upload to PyPI

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