Externalise SQL dialect specifications into an external file to simplify user contributions

[lukaseder]

Users start liking jOOQ for many reasons. However, some users would love to use jOOQ for a currently not supported SQL dialect. Extending jOOQ is a very difficult and demanding task. Maintaining support for "rare" SQL dialects is even worse.

If SQL dialect specifications could be externalised to a file, users could contribute more easily, which, in turn, would boost jOOQ's popularity.

This was also discussed here:
https://groups.google.com/forum/?fromgroups=#!topic/jooq-user/Nt7cc7QnFqI

[lukaseder]

This would make it too easy to circumvent jOOQ's licensing model. We cannot implement this.