Some undocumented functions and methods are now documented and tested.
Some doc tests were modified to become compilable, going from `ignore`
to `no_run`, or runable, going from `no_run` to regular tests.
This commit removes some unnecessary code, such as an extra `String`
clone, unnecessary `return` statements, and an inherent `to_string`
function for the `Regex` wrapper.
A double-quote character considered as a string literal by the
compiler was also changed to a single-quote character, this time
considered as a character by the compiler, for some optimization.
Also a newline is added in order to improve code readablitiy.
Rules are now a separate struct, and the `rules` member of
`settings::Settings` is now a `Vec<settings::rule::Rule`.
Several elements were made private, now can be accessed through
dedicated methods
