major, incorporate drbang (former dbnrbm) sources

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
hygiene, introduce const_layer_t and const_rbm_t and migrate inlines to them

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, move DEFSAMPLEF and DEFEXPECTF to maths.h

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
hygiene, rename internal slots for hidden and visible layers to hid and vis

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, let p(v | h) default to poisson distributions

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
revert c7c4d9d, that's a special case for the bottom layer only

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, provide make_dbn_stack()

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'feat/dbn'

* feat/dbn:
  minor, provide make_dbn_stack()
  revert c7c4d9d, that's a special case for the bottom layer only
  minor, let p(v | h) default to poisson distributions
  hygiene, rename internal slots for hidden and visible layers to hid and vis
  minor, move DEFSAMPLEF and DEFEXPECTF to maths.h
  hygiene, introduce const_layer_t and const_rbm_t and migrate inlines to them
  major, incorporate drbang (former dbnrbm) sources