Unary operations: Added math functions from C99.

The following new functions are now available:
 element_acosh()
 element_asinh()
 element_atanh()
 element_erf()
 element_erfc()
 element_exp2()
 element_exp10()
 element_log2()
 element_round()
 element_rsqrt()
 element_trunc()

Commit based on patch provided by Matthias Möller, authored by Andrzej Jaeschke <andrzej.jaeschke@gmail.com>
The original patch is extended to also clean up the CUDA backend -> less code :-)
C++11 guards are added to the tests.
Code compiles and tests run without C++11, but more testing desired to make sure everything is in order.