* Add new class SpecimenDimensions to hold dimensional information.
* Add stress variable to FrameData class.
* rename calc_stress function to read_file
* Add data filepath as input to read_file function
* read_file function now calculates stress from cross-sectional area
of specimen and load from each frame.
* read_file function now returns dictionary (indexed by frame number)
of FrameData objects that have load, displacement, and stress data.
Also returns SpecimenDimensions object that holds width, thickness,
gauge length, and overall length.
Created main.py with a function to read in the provided text file.
Gets specimen dimensions, frame number, load, and displacement data into
dictionary of FrameData classes.
