MAINT: Fix clang build and remove some unicode characters

[peterbell10]

When compiling with clang 10 or 11, I get errors in biasedurn/wnchyppr.cpp:

scipy/stats/biasedurn/wnchyppr.cpp:553:20: error: non-constant-expression cannot be narrowed from type 'int32_t' (aka 'int') to 'double' in initializer list [-Wc++11-narrowing]
   double xx[2] = {x, n-x};

On macOS, where clang is the default, this was fixed by adding a command line flag -Wno-narrowing. This PR takes the other approach of adding the appropriate static_casts.

Also, when editing this file I get invalid unicode character errors. So replaced those with plain ascii.

[rgommers]

Thanks Peter. LGTM - the extra compile flags approach isn't portable indeed. I'll defer to @mckib2 for the rest.

[mckib2]

These source files are vendored from the BiasedUrn R package version that was approved for use under the BSD-new license. We added the compiler flags to avoid modifying any of the sources as much as possible, but if there are portability issues that can't be easily solved via flags during the build, then I don't have any reservations about making changes. We can let the git history speak for itself as far as tracking what modifications we've made. The changes to use static_cast is indeed the right thing to here

[tylerjereddy]

Alright, two core dev approvals and CI fails don't look related.

[tylerjereddy]

Thanks @peterbell10 et al.