  * Implement mangle option:
    + Regex for mangling source content.
    + Repeated use of the option is merged together.
  * Implement id resolving:
    + For defined authors, us email address, URL, or full string as key.
    + Use fc when Unicode::CaseFold is available, else lc.
  * Implement merge-author option:
    + no: Disable id resolving altogether
    + yes (default): same as titlecase.
    + force: same as lowercase.
    + fail: die on author id referencing varying full strings.
    + titlecase: Merge id's varying only in case, Favoring titlecase
      over other mixed-case, lowercase, or uppercase (in that order).
    + lowercase: Merge id's always, lowercasing varying content.
  * Use Log::Any:
    + Emit warning when author id's refer to varying full strings.
  * Implement alias option:
    + Hash of arrays of id's to be merged with id used as key.
  * Fix "Complex regular subexpression recursion limit (32766) exceeded at /usr/share/perl5/String/Copyright.pm line 162."
    seen with twitter-bootstrap3 3.4.1+dfsg-1.
