Improve strict=True

[ecatkins]

I am finding that a number of correct date formats are failing to parsed by strict=True. I have made changed to to patch this in extract_date_strings_inner and I have also added a new test file to account for these, I don't think find_dates is being tested in strict mode under the current suite?

1. mm/dd/yyyy e.g. 09/06/2018
2. xxth day of yyyy e.g. 19th day of May, 2015 (NB: Had to change a spuriously passed test intest_extract_date_strings.py

[hmoravec]

@akoumjian This PR should fix the strict mode and it's been opened for more than a year. Would it be possible to merge it?

[akoumjian]

Only took me three years, but thank you!