Function plot_line() is not documented and also has some errors and typos

[realsdx]

In line 144 argument variable 'file_paths' should be 'file_path'
https://github.com/NITDgpOS/PlotIt/blob/master/plotit.py#L144

In Line 112 'options.line' should not be inside an else block.
In file 'plotutil.py' in 'plt.title' there should be no 'func' variable-
https://github.com/NITDgpOS/PlotIt/blob/master/lib/plotutil.py#L116

I already solved these issues .. should i do a PR now?

Also, the line plotting function should be documented.

[djmgit]

@realsdx Hi, thanks for looking into it. Please go forward send a PR :)