Update documentation

Addons to Gframe methods documentation

Update documentation

Added link to GitHub source code in every function in docs

Update documentation

inconsistency in default values in docs corrected

Update documentation

remove **kwargs from mean,std,cv,pcv,quantile,iqr

Update documentation

change "all days combined -> "the entire dataset"

Update documentation

change name of variable target_range -> interval

Update documentation

Update README.md

Update documentation

removed return type on utils func definitions

Update documentation

Added description to periodogram

Update documentation

added reference to DataFrame in intro.rst

Update documentation

Create Gframe from DataFrame on intro.rst

Update documentation

Update plot imgs

Update documentation

docs new section: Intro

Update documentation

doc new section: Getting Started

Update documentation

add rGV to README