SCONS-based build system to be used as base for gcc-avr projects.

Main features:
** Out of order build : keep your code and compilation objects nicely separated
** 'Heterogeneous' compiler settings : allows you to set different settings for each compilable. To make it even easier, an abstraction layer has been added to offer some preconfigured option sets (OPT_DEFAULT,OPT_SPEED,OPT_SIZE and OPT_DEBUG).
** Blazing fast : autodetects best suitable number for '-j #' option, speeding compilation process using all CPU cores available .
** 'make' integration : this step was not necessary, but simplifies deployment and help convincing your 'anything-other-than make' skeptical colleagues.
** Hierarchical build definition : no more "define all your compilables on a single file", you can define build-rules per module, isolating specifics if needed and creating a true hierarchical definition.
** Easy to use