trace-cmd: Implement a main functionality lookup table

Since now there is an uniform command implementation I can reduce the
 `main()` function to the minimum by using a lookup table. People can
 now directly focus on a command implementation because there is
 "nothing" in the `main()` function.

Link: http://lkml.kernel.org/r/20170426203028.13900-3-federico.vaga@vaga.pv.it

Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
4 files changed