Add variable MAX, numerically highest node type.
Addd Abase, A_st and A_lag as properties of LPModel
Add PrintConstraint to LPModel

Allows you to print any constraint in a nice, human readable format.
Refactor PrintConstraint and allow to print multiple constraints

1. Refactored to include a loop of the matrices of interest when writing
the constraint.

2. Code now allows for printing multiple constraints in one call.
Add documentation to PrintConstraint
Correct bug to print RHS correctly
Change string to use floating point output
Minor formatting changes
Write PrintConstraintFull, which expands out losses in the constraint

Function PrintConstraintFull is like PrintConstraint, but shows the
losses along in the incoming arcs directly, rather than printing a loss
variable.

Note, I havne't figured out a graceful way to combine PrintConstraint
and PrintConstraintFull into a single function with an option.