Case Insensitive Builder Feature Port

This is a small add-in to allow for options to be passed in as boolean values and mutate the Config through the RegexBuilder. This is primarily to align with the standard Regex crate for their own RegexBuilder.

Changes

• Added a field to the RegexOptions to keep a state of regex_automata::utils::syntax::Config internally to disseminate the proper flag overrides
• Added public method to Regexbuilder called case_insensitive
  - This will allow for forcing of a flag if not present in the raw str
• Added a call to the RaRegexBuilder which will consume this option using .syntax( ... )
• Added tests into lib.rs to make sure the override works as intended

Examples

Currently, we can write in flags into the raw string like this:

use fancy_regex::RegexBuilder;

let re = r"(?i)FOO BAR";
let regex = RegexBuilder::new(re).build()?;
assert!(regex.is_match("foo bar").unwrap_or_default());

This change is to enable builder functionality like this:

use fancy_regex::RegexBuilder;

let re = r"FOO BAR";
let regex = RegexBuilder::new(re)
	.case_insensitive(true)
	.build()?;
assert!(regex.is_match("foo bar").unwrap_or_default());

Notes

Currently, fancy-regex doesn't support flags such as (?-i) and that is likely something we should enable in the future. The correlation of that type of flag to this feature add ties to the builder case_insensitive setter method. This method should override any raw input data.