Added Uk sort code formatting and validation.

Added Uk sort code formatting and validation. Tests pass and demo in
place.
Added format and validation for time in years and months.

Especially useful for capturing duration information such as time at
location or in last employment position.
Update README.md
Fixed Uk Sort Code and added in the correct tests.
Added in extra tests for yy_mm. Changed validation method slightly to be more secure. Changed demo order as suggested.
Renamed `yy_mm` to `time_yy_mm` and added extra tests for valid inputs.
Fixing the backspace problem with both fields, and updated the demo ordering (yyyy_mm_dd was out of place)
Fixing field ordering the read me
Fixing spacing and indentation in the time_yy_mm field
Merging in master, still need to update time_yy_mm and uk_sort_code fields