This commit mainly introduces an almost-normal sysroot where the
compiler and libs will be installed. This is done in order to properly
build libstdc++-v3 from the GCC tree while also cleaning up the
slightly chaotic current install system.
* Add an `fxsdk --version` command
* Redo the README like a translation of the French topic
* Up default project to gint 2.9 to help get migrations right
* Add new `fxsdk path` command reporting important folders
* Add new CMake variables FXSDK_SYSROOT, FXSDK_INCLUDE, FXSDK_LIB so
CMake can access the information of `fxsdk path`
* fxSDK is now in charge of removing the entire sysroot including the
cross-compiler
* Add a LICENSE file
Version 3.15 introduces the <PREFIX>_KEYWORDS_MISSING_VALUES of the
cmake_parse_arguments() function, which is used in generate_g1a() and
generate_g3a(), so there is no way to bring it further down for free.
The FindPNG module fails catastrophically on Mac OS because it searches
for the library and header independently, and ends up pulling a
completely unrelated header from a random framework.
