changed isinteger, isreal, etc.

From discussion of #3054
- new ~~isela~~ `iseltype` function (I'm open to a better suggestion for the name)
- deprecate `isinteger`, `isreal`, `iscomplex`, `isbool`
- renamed `integer_valued`, `real_valued`, `float64_valued` to ~~isintegervalued~~ `isinteger`, etc. ~~(I didn't change it to `isinteger` as that could cause problems with existing code/matlab & octave users).~~: this is a breaking change.