Parsing oddities

[bjodah]

Parsing of strings silently accept some insane strings. Instead, it should raise an error. Examples:

>>> from chempy import ReactionSystem as RS
>>> RS.from_string("CO -> O + C ->").string()  # should raise!
'CO -> C + O\n'
>>> RS.from_string("COqasza -> Oqasd + Cqagdsfxxds").string()  # should raise!
'COqasza -> Cqagdsfxxds + Oqasd\n'