Use set_quote_char() to set the defaults

This keeps our regexes in one place instead of redefining them in
multiple places where it would be easy to modify one but not the other.
The set_quote_char() function itself is moved closer to the variables it
sets for readability.
Rename to set_quote_characters(); no need to use an abbreviated word
Move copyright and license POD to end of file so we can write inline function doc
Document the two publicized functions: extract and set_quote_characters