Support ARM `neon` SIMD

[V0ldek]

Is your feature request related to a problem? Please describe.
If the neon target feature is enabled and the arch is ARM, the SimdBlock size should be 16 bytes (128 bits).

Tracking issue: #17

Describe the solution you'd like
Change in the src/alignment/simd.rs file and a test asserting the size when compiled on ARM with neon enabled.