Add TODO detail directory.

doc/TODO.detail/README

doc/TODO.detail/alpha

doc/TODO.detail/arrays

doc/TODO.detail/cnfify

doc/TODO.detail/flock

doc/TODO.detail/fsync

doc/TODO.detail/lex

doc/TODO.detail/limit

doc/TODO.detail/logging

doc/TODO.detail/memory

doc/TODO.detail/nulls

doc/TODO.detail/optimizer

doc/TODO.detail/outer

doc/TODO.detail/performance

doc/TODO.detail/persistent

doc/TODO.detail/pg_shadow

doc/TODO.detail/prepare

doc/TODO.detail/primary

doc/TODO.detail/tcl_arrays