0.2.0
 - BREAKING CHANGES:
   - ref: changed submodule imports, please revise your scripts
   - ref: move computation of stress to stress.boyde2009 submodule
 - feat: added support for GGF look-up tables
   Note that an experimental look-up table is already included in
   the release on PyPI, but not yet in the source tree.
 - feat: analytical computation of GGF from Legendre polynomials
 - globgeomfact.coeff2ggf returned complex instead of float
 - docs: add preliminary theoretical part 
0.1.0
 - initial version
