Version 2.0, second alpha version

Second alpha release of the second major version of X-RAAS.
Changes:

• We have made embedding support explicit
• Much nicer facilities for external FMS integration (no need to modify the code, just use the datarefs)
• Dedicated Avionics Integration Guide pdf for aircraft devs.
• Shortened User manual by excluding dev-oriented portions.
• Documented new 2.0 features in user manual, notably the GUI and its options.
• Reorganized distribution ZIP package to remove top-level files which were unneeded and confusing.
• FreeType is now only rebuilt during ./build_release when its source package is updated.

Version 2.0, first alpha version

Initial alpha release of second major version of X-RAAS.