Use typedef's for the qadic types.
Misc qadic commit.

* Make qadic_val an inline function.
* Modify the sqrt code.
* Fix a bug in the trace code.
Small improvements to qadics documentation.
Small changes to qadic.h
Small improvements to qadic/test/t-frobenius.
Remove the function qadic_scalar_mod_ppow.
Small improvement to qadic exp/exp_rectangular.