Include/exclude printers from export to GCP...

Addresses #23 and #70.

Add options `-i REGEXP` and `-x REGEXP` to determine which local printers are included, respectively excluded.

For me, the big win is being able to say `-x GCP-`, which excludes all of my [CUPS cloudprint](https://github.com/simoncadman/CUPS-Cloud-Print/blob/master/README.md) printers.

`REGEXP` is a python regular expression.  REs are matched against the start of the printer name.  There can be multiple include/exclude options.

If there are no include/exclude options, then *all* printers are exported to GCP, as currently.

You can preview the documentation [here](https://github.com/smblott-github/cloudprint/tree/include-exclude#examples---includeexclude).