Document debug levels and debugging techniques

Submitted by pio..@..sf.net

Description

first off, is there any difference between the environment var GST_DEBUG and the commandline-option --gst-debug? if not then this should be mentioned. but the major issue here is that man-page merely mentions the possibility to increase debug level, and suggests to use --gst-debug-help to get more info. this way that option gets too little emphasis, which is strange for a tool that's supposed to be merely a sandbox for testing out pipelines. there certainly are parts that can be debugged and that do not depend on whatever external plugins. please make a choice of the most useful debug options and put them into the man-page with the GST_DEBUG or --gst-debug info. it's good to see some examples for gst-launch usage, but for a programmer more interesting would be to also see examples for how to learn more about what is happening under the hood. maybe also a section called troubleshooting could be added. there frequently asked questions could be addressed with some fitting debug-levels. in other words, please put more emphasis on the possibility of debugging within the man-page. at least to me, now that I know of this possibility, gst isn't as frightening a beast as it was before...