Add tabularx and other parameter options

[andersonfrailey]

Adds a number of new parameter options:

• column_escape: If true, escapes latex characters used in column labels. Otherwise leaves them
• index_escape: If true, escapes latex characters used in index labels. Otherwise leaves them
• use_tabularx: If true, wraps table content in a tabularx environment instead of tabular
• dependent_var_cover_index: Used in ModelTable. If true will extend the dependent variable name label across the index column as well as the estimate columns
• dependent_var_alignment: Used in ModelTable. Alignment to use for the dependent variable name label
• underline_dependent_variable_name: Used in ModelTable. If true, underlines the dependent variable name in the table

Also cleans up some comments and adds tests