[WIP] Big overhaul

Created by: carstenbauer

This is a WIP PR to improve the user-facing interface (and documetation) of, primarily, LIKWID.PerfMon.

Code

• one-based indexing
• provide simplified interface
  • perfmon
    • multiple perf groups
  • @perfmon
    • keyword args for autopin etc.?
    • multiple perf groups
• CI
  • check / overhaul / fix examples
    • CPU
    • GPU (and CPU+GPU)
  • setup CI on N2

Docs

• clarify examples wrt indices (not cpu ids, one-based)
• multiple group example
• multithreading example

TODO before merge

• tests for @perfmon_marker / perfmon_marker
• docs
  • howto perfmon
• @nvmon / nvmon
  • tests
• @nvmon_marker / nvmon_marker
• Update example in README.md