Added ability to input time dependent Hamiltonians to the 4op 2t correlator
Necessary in generating test functions (needs mcsolve fixes)
Added test functions for 4op 2t correlator when H is time dependent
Made small changes:
 - regular express
 -added reverse operator argument
 -attempted to change everything to PEP8
 -renamed shift function and a few variables
  -added old-style time dependence
  -shortened test functions
Ensured that create() returns a CSR type sparse matrix
Added CSR type checks for operators to tests
Fixed small error in operator doc strings
Tests to check states CSR type
fixed wrong dir for test script
Get fill factor of iLU preconditioner
Calculate preconditioning time.
fix bug in gate_expand_3toN for the case when N=3 and targets and controls are only permuted
added unit tests for testing permuting controls and target of 3-qubit gates
Merge pull request #211 from jrjohansson/bugfix-gate_expand_3toN

fix bug in gate_expand_3toN
Updated sparse bandwidth test with rand matrix
Function to calculate profile of sparse matrix
Added Lato import from google fonts
Minro changes to sparse profile
Added randomized sp_profile tests
FIXED: Sparse profile requires int64 dtypes

Ran into overflow issues giving negative results for profile on larger
problems.