removed wildcard handling to fix #71

Following the discussion from #71 here are the changes:
- disabled wildcard handling in Obis identifier comparison.
- added stricter handling on parsing codes to throw an exception if hex codes are used or invalid numbers.
- default Obis constructor now initializes with 0xff to be more in line with string parsing. 
- some more unit tests for obis
- added exception handling for MeterD0 around Obis string parsing. Invalid values will just be ignored but parsing continued. Later we could remove the strong restriction to only allow obis_codes starting with 1 or 2 (especially since all EDIS meter will report 255....) but somebody with a Landis&Gyr E350 needs to test this first.

I tested with my Hager EHZ361 and had no issues and no need to adjust my config file.
Please do intensive testing and let me know any issues.
Yes, even though I’m not happy with the „DC“. One hand it could be misread as 0xdc on the other hand it should be more a „not given“ (NG). DC sounds more like a wildcard. 
Anyhow I’ll change as well.


> Am 26.12.2014 um 12:39 schrieb andig <notifications@github.com>:
> 
> In src/Obis.cpp <https://github.com/volkszaehler/vzlogger/pull/78#discussion-diff-22282536>:
> 
> > @@ -136,12 +129,13 @@ Obis::Obis(const char *strClear) {
> >  }
> >  
> >  Obis::Obis(){
> > -	_obisId._raw[0]=0;
> > -	_obisId._raw[1]=0;
> > -	_obisId._raw[2]=0;
> > -	_obisId._raw[3]=0;
> > -	_obisId._raw[4]=0;
> > -	_obisId._raw[5]=0;
> > +	// to be more consistent we initialize with DC/255.
> Should use DC instead of 255?
> 
> —
> Reply to this email directly or view it on GitHub <https://github.com/volkszaehler/vzlogger/pull/78/files#r22282536>.
> 

Gruß

Matthias Behr