edit MDComparison._comparison_check()

comparison checks for dates and numbers now
update .gitignore

ignore dev script
change MDComparison.value to predicate

better semantics
clean up get_all_attributes

remove grouping steps
move date parsing to _parse_date_value

function is now self contained
add check for numbers in MDComparison.format()

properly handles number predicates now when formatting
make all module level names private

when dynamically generating attributes, all vars used are double private
add attributes.all attr

attributes.all returns names of all attributes dynamically defined; set to `__all__`
remove double underscores

`convert_camel` now cleans up double underscores