added support for counting field in liouvillian operator
new module for counting statistics
added functions for computing pseudo_inverse
pep8 fix
Merge branch 'master' into counting-statistics
Merge branch 'master' into counting-statistics
changed function signature of countstat_current
improved pseudo_inverse and updated its docstrings
pep8 fixes
updated functions signatures
updated docstrings
reorganized imports
add countstat to  imports
docstring grammar fix
fix import errors
use approach cleverly suggested by paul
pep8 fixes
code cleanup and docstring updates
resolved merge conflicts
updated function signature and added input parameter tests