Vagrant environment and explaination of the examples

[fntlnz]

Opening this PR to address the concern that many readers had about being able to compile and run some of the examples.

This contains:

• A Vagrantfile containing all the needed dependencies to compile and execute the examples
• Updated the Readme with instructions for the Vagrantfile and for getting a copy of the kernel source
• Make sure all the examples work and have a matching description to complement the book
  • Hello World
  • Kprobes
  • Kretprobes
  • Uprobes
  • Uretprobes
  • Tracepoints
  • User Statically Defined Tracepoints
  • Flame Graphs
  • Histograms
  • Perf Events
  • Packet filtering for raw sockets
  • Traffic control classifier program using cls_bpf
  • XDP using iproute2 as a loader
  • XDP using BCC as a loader
  • Testing XDP programs
  • Seccomp BPF filter example

[fntlnz]

I will merge this and open a new issue for the remaining examples!