Fix extra indentation level in Money#extract_cents
Rename used_decimal_marks to used_delimiters

  - When extracting everything but digit characters, the values extracted
    have only a general delimiting purpose instead of decimal mark
    separators.
Fix misuse of thousands_separator and decimal_mark variables.

  - Scanning from the most significant part of the value to the least
    for non-digit values will return thousands_separator and decimal_mark
    in the corresponding order (instead of reverse).
Merge pull request #253 from jgakos/extract_cents_naming_fix

Extract cents naming fix