v0.8.2

Bug fixes:

• Fixed MadminerParticle initialization by using @ classmethod helpers. Thanks @lyazj.
• Replaced MadminerParticle inherited class (VectorObject4D -> MomentumObject4D). Thanks @lyazj.
• Bumped vector package to version 0.8.4, first version to properly allow subclassing.

Internal changes:

• Replaced Python2 compatible super-class calls by Python3 style.

Documentation:

• Fixed README relative links (unavailable on Madminer's PyPi information page).