Regex Validation

[FreeMasen]

• [x] Validate Flags are only "g", "i", "m", "u", or "y"
• [x] body cannot start with "*"
• [x] flags cannot contain duplicates
• [x] body must be pattern link
• [x] look behinds
• [x] "u" flag disables "quantifiable assertions"
• [x] unicode escapes must be hex values
• [x] class ranges cannot contain multi character set i.e. [\d-\s] is invalid