Refactor private functions

    - Closes #243
    - Use null instead of nil (closes #234)
    - Ignore case for string variables (closes #235)
    - Remove extraneous @else (closes #237)
    - Use is-even where appropriate (closes #238)
    - Remove ternaries (closes #239)
    - Remove camel case (closes #240)
    - Refactor is-display-table (closes #241)