Bump version to 0.9.21

Fixes:
- CORSIKA coordinate transformation
- celestial transformations
- particle query for groundparticle simulations
- bug in errorless simulations
- more tests for some parts

setup.py

@@ -2,7 +2,7 @@
 
 
 setup(name='hisparc-sapphire',
-      version='0.9.20',
+      version='0.9.21',
       packages=find_packages(),
       url='http://github.com/hisparc/sapphire/',
       bugtrack_url='http://github.com/HiSPARC/sapphire/issues',