DOC: more consistent use of backticks throughout _multilevel.py
DOC: more consistent use of backticks throughout _multilevel.py

PyWavelets/pywt,PyWavelets/pywt,rgommers/pywt,grlee77/pywt,rgommers/pywt,rgommers/pywt,rgommers/pywt,grlee77/pywt