Added support for SQL conversion

[smuellner]

Added two converters for SQL inserts and updates

[smuellner]

There have been now some more changes, but overall I feel final to merge back.
The PR now contains a change to the main countries.json introducing a unique id for every country (ucid) to allow for updating the countries in a database.

[mledoze]

Hello, thank you for your work, I will look into it this week.

[smuellner]

Hello, thank you for your work, I will look into it this week.

Thanks a lot for your work and idea on this repository, it did help me very much with getting a good head start.
If you need changes or input I would be very happy and glad to provide them.
For the necessary change adding a unique country _id, it would be very nice to have your insight if there would be another approach possible instead of using an ordinal number. I did thought about the country code but as this is not provided for all countries it was not a good fit. Any other value seemed to be not constant and subjected to change or it felt not a good fit as a unique database ID at all.

Thanks again and have a great week,
Sascha