Increase support for time-series and regressions (Python)

ArviZ is a Python package for exploratory analysis of Bayesian models, intending to provide backend-agnostic tools for diagnostics and visualizations of Bayesian inference in Python. There are currently no specific plots in arviz to visualize time series or regression models. My proposal is to add time series plots including line and scatter plots to the library to visualize the uncertainty in the actual data vs the range of predicted data. Dataset is assumed to be provided by the user. The project includes the documentation of functions implemented and examples for each of them.