Radioactivedecay

- Fixed bug in `InventoryHP` meaning `decay()` gave some incorrect results.
- Hard-coded Avogadro's constant to avoid tests failing with older versions of SciPy.
- Updated notebooks to be consistent with v0.4.0+.

- Added ICRP-07 and AMDC license files into MANIFEST.in. Includes these files in PyPI package.

masses, moles and numbers of atoms when creating inventories, and also methods so inventories can
report their contents in terms of these quantities, as well as mass or atom fractions (35). Mass
conversions use atomic mass data from the Atomic Mass Data Center (AMDC) by default.
- To enable SymPy high precision calculations throughout unit and quantity conversions, there is a
new `InventoryHP` class (high-precision inventory class). This behaves the same as the normal
precision `Inventory` class. The old `Inventory.decay_high_precision()` method is now deprecated -
use `InventoryHP.decay()` instead for high-precision decay calculations.
The number of significant figures for high precision decay calculations is now specified via the
`InventoryHP.sig_fig` attribute (default is 320) rather than as a parameter to the `InventoryHP`
`decay()` and `plot()` methods.
- Added new `cumulative_decays()` method to the inventory classes. This calculates the total number
of atoms of each radionuclide that decay over the decay time period.
- Added support to specify nuclides using canonical ids (36).
- Documentation updates for all new and modified functionality.
- LICENSE file split into separate files for `radioactivedecay`, ICRP-107 decay data, and AMDC
atomic mass data (38).
- Added parsing of AME2020 and NuBase2020 atomic mass and isomer excitation energy data to ICRP-107
dataset Jupyter notebook. Added stable nuclides to decaydata.npz file, C and C_inv matrix SciPy
and SymPy files in ICRP-107 (33 & 34).

- Fix bug in decay chain plots which caused overlaps of some radionuclides in complicated chains.
- Document method for installing via conda.
- Improve clarity of matplotlib imports.
- Correct a DecayData attribute docstring entry.

- Improve readme and fix typo.
- Add MANIFEST.in so LICENSE and markdown files get packaged.
- Update year in LICENSE file.

- Allow specification of `sig_fig` as a parameter to the `decay_high_precision()` method.
- Improve code with respect to pylint and mypy checks.
- Add discussion on the radioactive progeny that are not in the ICRP-107 data to the limitations
section of the docs and to the Jupyter notebook analyzing the ICRP-107 data.
- Update other Jupyter notebooks for this release.
- Theory docpage typo fix.