Domain Calculation

Started the domain calculation file (domain.py) and made the function get_constraints() that recurses through the tree to look for domain restricting operators like /, sqrt, log, arcsin, etc. into a list. next steps are to solve each of the generated constraints (inequalities) and then combine them to get the domain for x (or any variable).

Currently working on trying to solve the inequalities but it is proving to be pretty difficult so it could take longer than usual.