Add is_aligned for both C and C++ APIs

[vianney-st]

// C
int is_aligned(const void* const ptr) {
#if NSIMD_WORD_SIZE == 32
const u32 val = (u32)ptr;
#else
const u64 val = (u64)ptr;
#endif
return val % (NSIMD_MAX_ALIGNMENT / CHAR_BIT) == 0;
}

// C++
template<typename T>
bool is_aligned(const T* const ptr) {
#if NSIMD_WORD_SIZE == 32
u32 val = (u32)ptr;
#else
u64 val = (u64)ptr;
#endif
return val % (NSIMD_MAX_ALIGNMENT / CHAR_BIT) == 0;
}