0.5.2

• Added new functionality vec2df to create dataframe from source-target-weights
• Added new example to demonstrate the usage
• updated some docstrings

Example vec2df:

import bnlearn as bn

source=['Cloudy','Cloudy','Sprinkler','Rain']
target=['Sprinkler','Rain','Wet_Grass','Wet_Grass']
weights=[1,2,1,3]

# Convert into sparse datamatrix
df = bn.vec2df(source, target, weights=weights)

#    Cloudy   Rain  Sprinkler  Wet_Grass
# 0    True  False       True      False
# 1    True   True      False      False
# 2    True   True      False      False
# 3   False  False       True       True
# 4   False   True      False       True
# 5   False   True      False       True
# 6   False   True      False       True