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.

Some bug-fixes and improvements

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

Available values in queue are only published if their number is >= minValues

Minor improvement to MQTTPusher so it does not crash if CollectAgent goes offline but instead tries to reconnect later

Outsourcing of sysfspusher.cpp into multiple classes is now complete

Minor fixes to SYSFSSensor