remapper: properly relay signal to tracee
remapper: exit when tracee exit
rempapper: move macros in debug.h
remapper: nice logging level names
remapper: fix logging messages removed ifdef DEBUG
remapper: use env variable to set logging level

It is now possible to use REMAPPER_DEBUG to set the debug level
If the value of the variable contains:
 - "info"     it will display informational messages
 - "event"    it will display event messages
              (relative to ptrace and wait)
 - "mapping"  it will disaply messages relative to file path
              remapping