Update license file with new copyright dates.
Removed extopts library sources.

Now embox will link extopts dinamically.
Starter code is simplified to check direct link against extopts.
Added AUTHORS file.
Build reimplemented with cmake.

Notes:
- current build is broken. It will not find extopts library. For
  hardcode purposes option '-lextopts' may be added into
  CMAKE_C_FLAGS. The correct way - write find_package module for
  extopts (must be implemented soon);
- currect versioning on base of git info is commented-out. Must be
  tested and enabled back.
Gitignore config update.
Find extopts cflags from pkg-config.

The ugly way. Added only for extopts pkgconfig file testing. Better be
used PkgConfig module for such matters.