add instruction for new comers about supported excel versions
use double.Parse with invariantCulture (avoid silent fails do not use Try)
be more inclusive while unregistering keys in uninstall. Wipe out both 32 and 64 xll's OPEN HKCU keys.

Add comment about a tricky situation where user may have change of Office version (32 to 64 or conversly)
missing namespace for commit 0c146e8b075cdbf30a9ea20602d6e1be0a491df4