[lttng-dev] Expose kernel tracer to user-space

[Francis Giraldeau]

This series of patch follows the discussion about exposing kernel tracer to
user-space. Here are few highlights:

  * Creates one lttng_uevent kernel event by writing to /proc/lttng
  * The event is a variable size byte sequence, parsed by default as UTF-8 text
  * Uses already existing /proc/lttng file instead of creating another
  * Refactor the tp_memcpy macros to support sequence and copy_from_user