[ENH] Update nuclear g-factor data

[lmmentel]

• update g-factor values and their uncertainties

Fixes #97

Proposed Changes

• updated data for g_factor and g_factor_uncertainty for isotopes from the latest source Table of Recommended Nuclear Magnetic Dipole Moments: Part I - Long-lived States and updated docs

Example

After the changes, previously missing values are now available, for example:

from mendeleev import K, Ti, Cr

K.isotope(40).g_factor
-0.32449251413345337

Ti.isotope(47).g_factor
-0.3152559995651245

Ti.isotope(49).g_factor
-0.31534287333488464

Cr.isotope(53).g_factor
-0.3162066638469696