Add Cuba implementation which compiles to shared library.

Obtained as submodule from https://github.com/JohannesBuchner/cuba.
To compile shared library, in deps/cuba run ./configure, then
cp makefile.shared makefile. Then run make.
Add Cuhre test and begin to correct wrapper implementation.

Data seems to get into Cuhre OK (Cuhre prints the correct integral values),
but the return values cannot get back out to Julia.

Always get 0 back for the integer return values nregions, neval, fail.
Using the suggestion from the Julia manual to declare these variables by
nregions = Int32[0], etc. and dropping the associated & in ccall causes
segfault. Also fail to get values back for integral, error, and prob.
Integral always is set to [-999.0, -999.0, -999.0] in test; error and
prob contain 0.0's.