documentation fixes
remove unused stuff
rename MGL-TRAIN to MGL-CORE
split off MGL-DATASET package
move segment stuff to MGL-OPT
more docs for @MGL-OPT-EXTENSION-API
fix mnist dbm
fix example cg monitoring
:SAMPLER -> :GENERATOR
add MAKE-RANDOM-SAMPLER
document weight I/O
shuffle packages around
document stripes
reexport everything from the MGL package
document stripes, executors
indent MGL-GNUPLOT docstrings
documentation tweaks
rename train.lisp to core.lisp