Fixed building failure with Visual Studio 2015

[johnnychien85]

First compiler error found here:
cpu_x86.h(42): error C2556: '__int64 fbow::cpu_x86::xgetbv(unsigned int)': overloaded function differs only by return type from 'uint64_t fbow::cpu_x86::xgetbv(unsigned int)'

I checked the definition in line 36 of the same header:
static inline uint64_t xgetbv(unsigned int x);
and resolved this issue by changing the return type from uint64_t to uint64_t.

The second error is:
cpu_x86.h(71): error C2653: 'cpu_x86': is not a class or namespace name
which is due to the } in line 61 that prematurely closes namespace fbow{.

The third error encountered:
src\fbow.cpp(150): error C3861: 'aligned_alloc': identifier not found
is fixed by using _aligned_malloc instead of aligned_alloc. I added
#ifdef WIN32
#define aligned_alloc _aligned_malloc
#endif
to the header fbow.h to get rid of that one.