add line/cell magic

[DeanLa]

Brief Description

Inside a notebook have the option to make dovpanda only work on selected cells with cellmagic

example:

%%dovpanda
df = pd.concat((df1,df2))
df.iloc[0,0]

%dovpanda df = pd.concat((df1,df2))

[DeanLa]

Never created notebook magic, may require research. @galbraun what do you think?