Added a formatter

Will hopefully one day close #116 (closed).

Things to do:

• Use an AST (abstract syntax tree) for formatting instead of compiling and then decompiling again
• Write to the file by opening it with argparse.FileType("rw") instead of using open()
• Allow directories containing blp files as input
• Actually use the AST built to insert whitespace at the right places
• Handle comments properly
• Differentiate between child types and lists and format them accordingly
• Add LSP integration
• Newline between closing token and property
• Support item (label, action, icon) syntax
• No newline between comments and lines with opening tokens
• No whitespace/newlines between } and ;
• Cleanup
• Refactor & denest for readability