different approach to find out what was set explicitly
support day-, day+month-, time-only since
make since and till more intuitive when inputting partial dates
complete the case for when Month and Year are given
style: ensure two-line distance between defs
add to .gitignore: .pyc-files
extract datetime helpers to new datetime_helpers.py
allow time delta synonyms
rid off convert_to_timedelta's big if-statement
fix: parse_info had inconsistencies
update todo-list