Implement a keyword to search for SLGs based on next update date #52

Is your feature request related to a problem? Please describe.
We can now filter sherlock results based on next update date. Unfortunately, the filter text that Epic decided to use looks for SLGs using their internal date representation (days since 1/1/1841). I would much prefer to use dates in my locale format or using the date mnemonics.

Describe the solution you'd like
uw slg nu:T+7->T+14 returns all SLGs that have next update dates beginning with seven days from today and ending 14 days from today.