detection for allday events with no VALUE=DATE

this should fix github #95 partly
understand EXDATE with another TZINFO than DTSTART

this should fix github #95 partly
handling rec. events with unsupported exceptions

these events won't be inserted into the db at the moment, instead a
warning will be printed

see https://github.com/geier/khal/issues/97
Improve validate function
removed keychain for extra requirements
BROKEN started to move to configobj based configuration
refactoring (config is now dict, not namespace)
reenabled config dumping
we need to write to cli config tests
check for valid timezones
forgot to check in settings/utils.py
better testing of config
BROKEN first config test
first tests for settings
started working on configuration doc
documenting khal's configuration

most parts of the documentation on khal's configuration are actually
auto-generated from the spec file
log extra values in the configuration file
told configspec and with that doc about [sqlite] in config file
doc: make configspec.rst via Makefile
doc update