guix manifest upgrade and bug fixes

guix: added support for guix package/development

version bump
fixed memcheck enabling when valgrind missing

Bugfixes

Fixed recur across year/month boundaries not working properly
Improved timezone handling
Fixed prune not re-adding recurring events
Refactored recur functionality into own function

Completed v1.0.0 functionality

-Added optional arg to --upcoming (default = 1W)
-changed duration to until
-added man page
-added some minor color/formatting to ls
-added bash completions

Intial design complete

Full project completed.

Added the following sub-commands:
-add
-dismiss
-ls
-rm
-postpone
-prune

Added unit tests to verify functionality.

project creation