(also ensures compatibility with the macro)

(that package is giving serious npm vibes)

This potentially saves a lot of headache with various custom functions or stuff
where support may be complicated/ambiguous. In this precise case, we're
allowing it because the user needs to `@register` the factorial function with
Symbolics manually, so that it can be translated properly.

parse out and test specially marked time math

Closes #54

bump version to 0.5.0

import `download` from Downloads

add initial concentration, fix certainty of units

document the converter usage

support relational operators in math

add reversible flag

...to allow distinguishing stuff like Euler's number from variable name `e`

add support for running SBML converters

merge cleaned-up #49

not sure if you wanted to get rid of `Model` too, happy to revert that one

efficient cronless tagbot trigger

Added vscode gitignore line

add specs for codecov