Add new rule for detecting unnecessary escaped characters in regexp

[AdamWr]

Sometimes some characters can be escaped when it's not necessary. For example it's not necessary to escape + in:

/\/[a-z0-9]{12}\/[a-zA-Z0-9\/\+]{1,10}$/

so it could be rewritten as:

/\/[a-z0-9]{12}\/[a-zA-Z0-9\/+]{1,10}$/