bump 1.2.2

add SBML name accessors, bump SBML compat

Add `names` field to genes, metabolites and reaction types.

add citation information

GRR IDs may contain underscores

...which seems logical as they are interpreted as normal identifiers in matlab.

postpone JuMP 0.22 compatibility

This would break most of the tutorials and notebooks before Tulip issue #112 is
addressed (see https://github.com/ds4dm/Tulip.jl/issues/112).

COBREXA should be a dep of documentation Project.toml to enforce version checks

Build docs on PRs to master (to catch doc errors)

improve macro-related documentation

Update the dind version in CI (was: fix dind in CI)

bemp a small patch release

clean up some leftover unions with Nothing

- macro-generated functions get properly recognized by documenter and placed to
  the right section
- the generating macros have at least a bit of docs

Closes #508

explain the multi-gene knockouts better