Micom

Improves version compatibility with cobrapy and QIIME 2.

Fixed a bug where incorrectly labeled biomass demand reactions were treated like an
exchange.

Lowered the required version for pandas to re-enable compatibility with Python 3.6.

Docs are now built on all pushes.

`atol` and `rtol` are now consistently exposed.

Remove six dependency.

Got a bit smarter in cleaning up compartment suffixes. This fixes the odd "_e_m" suffix
in CARVEME-derived models. This will change the names of exchange reactions compared
to version 0.21.x.

Stabilize minimal_medium a bit more.

The strategy to calculate fluxes in the grow workflow can now be set with the
`strategy` argument. For instance, you can now get fluxes via parsimonious FBA instead of
assuming minimal imports.

Fixed a bug where minimal media classification with `weights="mass"` would fail due to
invalid elements in the formula (for instance "X").