Feat/past key lookup (#18)

* update Get methods to include a new parameter for lookup date and straight lookup

* update contructor value lookuptime

* added test for new features

* updated documentation and fixed casing parameters

* fix parameter names

* added getkey features

* a option to interpter your key without processing during set

* added new functions

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Co-authored-by: Laurent Aerens <laurent.aerens@telenet.be>