Add mention of the SERIAL data type. Change claim of "no limit" on maximum date for datetime type to  more realistic 1465001 AD. Thanks Tatsuo for pointing this out :) Clean up markup.
Add mention of the SERIAL data type.
Change claim of "no limit" on maximum date for datetime type to
 more realistic 1465001 AD. Thanks Tatsuo for pointing this out :)
Clean up markup.

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