Added preset styles and a way to add custom styles

[DenverCoder1]

Version 0.1.1

Fixes #2

• Split file structure into multiple parts
• Added TableStyle class for storing info about a theme (all the different parts that make up the table)
• Added PresetStyle class with pre-made styles to choose from
• Made a list of styles in /style_list and a script for generating the list
• Ensure that user-specified column widths are at least as large as cell contents
• Made header, body, and footer positional arguments (can place with no label); all other options must be keyworded.