Add new sensor functionality stopPolling(): stops collection of sensor values until startPolling() is called again

Partially revert last commit: Remove Logging file; instead every class/object gets his own logger as member-variable

Also fix 2 compiler warninge (signed-unsigned compare)

Reintroduce -v command line option
Reworked (partially reverted to previous state) how cmd-line options and global config-options are read in

Every sensor stores its full MQTT-topic now

Add possibility to compile with symbol DEBUG (use "make debug")
Minor fixes and improvements to debug-output

Finished rework of sysfs-files.
Adapted and improved various other involved classes.
TODOs remaining:
-adapting Makefile for automated compilation of librarys
-solving runtime errors when trying to run dcdbpusher with sysfs

Add generic Sensor-base class
Rework dcdbpusher + MQTTPusher to use generic base class

(former only one PerfCounter for all CPUs)
Add check if MQTT-Topic is assigned twice

Deleted test.c as it was just a reminder-file.
Add readme.txt as kind of (incomplete) documentation
Various TODOs remain. Also some polishing could be required.

Most of the code is copied from sysfspusher and adapted to match perfpusher
TODO: think of a suitable config-file-layout
TODO: insert new code to read perf-counters