use dict keys as state variables in synthesize_many
use dict keys as state variables in synthesize_many

to give the user full freedom to choose their variable names.
Improve associated docstring.
necozay/tulip-control,tulip-control/tulip-control,necozay/tulip-control,tulip-control/tulip-control,necozay/tulip-control,tulip-control/tulip-control,necozay/tulip-control,necozay/tulip-control,tulip-control/tulip-control