v0.7.0

SBML v0.7.0

Diff since v0.6.0

Closed issues:

• Adding substoich and prodstoich fields to Reaction (#119)
• test suite case 00198 fails (#133)
• DocStringExtensions usage (particularly on structs) (#136)
• SBML doesn't respect math rationals (#140)

Merged pull requests:

• support for logical operators (#135) (@exaexa)
• docstringextensions (#137) (@anandijain)
• rational mathval (#141) (@anandijain)
• separate reactants and product stoichiometries (#142) (@anandijain)
• Make sbml slightly more type-stable (#144) (@giordano)
• Fix definition of units (#145) (@giordano)