Function input feature for time-dependent boundary conditions

[ncdorn]

Current situation

given that @kharold23 has left the lab I have decided to take over #108. I have rebased this branch and now we can compare changes. thanks to @kharold23 for doing most of the heavy lifting on this a while back. There are extensive changes here so a code review may be in order.

Release Notes (from #108)

• Added a new parameter fn to flow and pressure boundary conditions that takes in a string
• Interprets the string as a function of time, represented by the variable t
• The value of the boundary condition is calculated at each time step by evaluating the function at t = the current time value.

Documentation

Time-dependent boundary conditions can now be input using a function passed in as a string. The function is of the variable t, or time. For example:
"bc_values": { "fn": "2.0 * (4*atan(1.)) * COS(2.0 * (4*atan(1.)) * t)" }

Testing

Test case test_time_dependent_block added to test_io.py, which runs json files timeDep_Flow.json and timeDep_Pressure.json.

Code of Conduct & Contributing Guidelines

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