ENH add_dummies helper
DOC: update docs on history values
DATA replace variable hours with last week's
DATA: move fix_edu_bug to helpers and call with read_long
DATA: filter out 0 earnings and hours
DATA/PERF: replace catagorical flows before writing
DATA/REF: add quarter chunking into make_long
BUG: fix replace_categorical to invert the dicts
ENH: add demo dummies and bin_education