Add counter for pending tasks to sensors. Wait until all tasks are finished before deconstructing anything

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

(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

Move configuration parser to new class Configuration. Add configuration parameters for IPMI session timeout and retransmission timeout.