Unified Date Handling role

'lo all,

Following on from the excellent work by @mwmiller to wrap calculator and numbers into a role, We've done the same with date handling (to address things like this https://github.com/duckduckgo/zeroclickinfo-goodies/issues/513). 

Not complete yet, however the goal will be to produce two public methods, `date_regex` and `parse_date`;
`date_regex` will output a massive regex for all the supported date formats, if they "look like dates"; but not guaranteeing that they're correct. I.e. 2014-02-31 would probably pass the match. 
`parse_date` will probably return a `DateTime` of the parsed date

Also, forgot to mention; Perl automatically "does what you want" when you concatenate regexes like this. I.e. if you do 
```
$a=qr/([0-9]+)/; $b=qr/([A-Z]+)/;
$c=join '|', ($a, $b);
```
then $c is magically: `qr/(?:([0-9]+)|(?:([A-Z]+))`