libmorton v0.2.2

Minor change:

• Only include BMI/AVX2 headers when needed
• Removed unused math.h header

libmorton v0.2.1

Minor change:

• Thanks to a PR from chris0x44 libmorton should now be easier to include.

libmorton v0.2

I'm starting with release versions, so I can indicate big changes. So here you go, the first version is v0.2. Because reasons. Enjoy!