Prefer Dates From Future only when specific words in date string

- Default to looking at dates from past, as most notes are from past
- Look for dates in future for cases where it's obvious query is for
  dates in the future but dateparser's parse doesn't parse it at all.
  E.g parse('5 months from now') returns nothing

- Setting PREFER_DATES_FROM_FUTURE in this case and passing just
  parse('5 months') to dateparser.parse works as expected

tests/test_date_filter.py

@@ -26,6 +26,10 @@ def test_parse():
     assert date_filter.parse('this year', relative_base=test_now) == (datetime(1984, 1, 1, 0, 0, 0), datetime(1985, 1, 1, 0, 0, 0))
     assert date_filter.parse('20 years later', relative_base=test_now) == (datetime(2004, 1, 1, 0, 0, 0), datetime(2005, 1, 1, 0, 0, 0))
 
+    # specific month/date variation
+    assert date_filter.parse('in august', relative_base=test_now) == (datetime(1983, 8, 1, 0, 0, 0), datetime(1983, 8, 2, 0, 0, 0))
+    assert date_filter.parse('on 1983-08-01', relative_base=test_now) == (datetime(1983, 8, 1, 0, 0, 0), datetime(1983, 8, 2, 0, 0, 0))
+
 
 def test_date_filter_regex():
     dtrange_match = re.search(date_filter.date_range_regex, 'head dt>"today" dt:"2020-01-01" tail')