Use map for configuration variable names
Use map for configuration variable names

Use a map instead of dozens of hardcoded conditionals. This makes
configuration variable parsing more dynamic and extensible.

Also, reintroduce formatting error messages that we dropped earlier.

Signed-off-by: Lukas Fleischer <af90e31281d8305af43dc616c5aaca3c7165f8a7@cryptocrack.de>

dunecn/calcurse,lfos/calcurse,dunecn/calcurse,lfos/calcurse,lfos/calcurse