Changes done:
* Added usage/configuration info for this mode.
* Created `tools/srcgenerator.py` to allow source/header generation
without using CMake.
* Adapted CMake to use the `srcgenerator.py` script.
* Added jerry-libm single-source build.
* Improved the `srcmerger.py` script to correctly handle the line numbering.
JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.u-szeged@partner.samsung.com