Initial "feature-complete" version

This MR adds several major changes:

• Change of build system to CMake
• Removal of duplicated source files: omp-tools.h, glib GTree
• Implementation of basic event set, inspired by the events that Extrae's legacy tracer produces
• Selective tracing: User can configure which events are enabled
• Link to Source: Experimental feature providing source locations for some events
• Elaborate README explaining the design, usage and event semantics
• Removal of the 'printer' tracer

Missing for now:

• Support for tracing OpenMP Target Offload applications