JamesPHoughton/pysd: 2.1.0

Allow working with Vensim models with regular DATA declaration, reading the data from a csv or tab file when loading the model. Giving several options to the user. Allow comparing two files with missing values and return True if the missing values are at the same place. Allow running submodel or the current model, selecting it by variable names or modules (produced when translating a file per views). Bug fixes. Improve and update documentation