qnumeric.h is undocumented and has no uppercase name, despite being public

The floating-point utility functions in qnumeric.h are very useful, but they have no documentation - and that makes them very hard to find. Additionally, the header has no uppercase name (QtNumeric), unlike other installed non-class headers (such as QtGlobal). Marius noted that qnumeric.h should probably be special-cased in syncqt, as some other headers are.