Add seekAfter() and seekBefore() to allow for paging in both directions

[lukaseder]

The SEEK method is currently only partially implemented, i.e. it allows only for fetching the "next" page. In order to fetch the "previous" page, a similar seekBefore() method could be introduced.

What's interesting is that the "seek method" is also referred to as keyset paging:
http://stackoverflow.com/a/3215973/521799

The jOOQ manual and blog should establish both terms, although SEEK is the preferred term in the API and synthetic SQL clause.

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Note that the existing seek() will be a synonym for seekAfter()