use nested config instead of flat one

This changes the config to a nested structure, so the default JSON looks like this:

```
{
	"newline":  {
		"before_brace": false,
		"before_extends": false,
		"before_implements": false,
		"condense_multiple": true,
		"empty_at_end_of_file": true
	},
	"space":  {
		"after":  {
			"type_hint_colon": false
		},
		"around":  {
			"additive_operators": true,
			"arrow": true,
			"assignment_operators": true,
			"equality_operators": true,
			"logical_operators": true,
			"multiplicative_operators": true,
			"relational_operators": true,
			"unary_operators": false
		},
		"before":  {
			"catch_keyword": true,
			"catch_left_brace": true,
			"catch_parenthesis": true,
			"else_keyword": true,
			"else_left_brace": true,
			"for_left_brace": true,
			"for_parenthesis": true,
			"if_left_brace": true,
			"if_parenthesis": true,
			"method_call_parenthesis": false,
			"method_declaration_parenthesis": false,
			"method_left_brace": true,
			"switch_left_brace": true,
			"switch_parenthesis": true,
			"try_left_brace": true,
			"type_hint_colon": false,
			"while_keyword": true,
			"while_left_brace": true,
			"while_parenthesis": true
		},
		"between":  {
			"call_arguments": true,
			"enum_arguments": true,
			"function_arguments": true,
			"type_constraints": true,
			"type_parameters": true,
			"var_declarations": true
		},
		"within":  {
			"catch_parenthesis": false,
			"for_parenthesis": false,
			"if_parenthesis": false,
			"method_call_parenthesis": false,
			"method_declaration_parenthesis": false,
			"switch_parenthesis": false,
			"ternary_after_colon": false,
			"ternary_after_question": false,
			"ternary_before_colon": false,
			"ternary_before_question": false,
			"while_parenthesis": false
		},
		"condense_multiple": true
	}
}
```

I've updated the demo accordingly to use `<ul>` for subsections. It's fairly ugly, but can be made to look nicer than the flat config by someone with the appropriate CSS skills.