This is a first step to clean up several compilation units and separate
the front end from back-end operations. All functions that require user
interaction are moved to a new compilation unit "interaction.c". Also,
following things are adjusted to the new layout:
* Make day_item_get_*() and a few other functions public, so that it can
be accessed from the new compilation unit.
* Use apoint_hilt(), todo_hilt(), etc. instead of directly accessing
static variables.
Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>
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