[Feature] ASCII table output

[joshua-white]

What is the requested feature? Write an AsciiTableOutput class derived from OutputBase that takes an array2D and writes it to output, using path checking and sanitation features from OutputBase. This can replace the TriaxialDriver's direct output, and may be useful for writing solver statistics, etc.

Alternative would be use HDF5 output, but for some data a direct-to-text approach will make the user's life easier.