Add UriPrintConnector

[mike42]

This adds the UriPrintConnector contributed by @evsar3.

Reference:

• Connect to printer using URI - determine connection type from scheme #314

[mike42]

I've refactored this to add tests.

I've also reduced the scope to URI schemes that are likely to work as expected in escpos-php. Things like IPP (not actually supported in CupsConnector) and lpt (not a real URI scheme, depends on client platform) have been taken out so that this feature does not have a negative impact on usability.