Add notebook autosetup and fetch utility for notebooks ...

[mmcky]

This PR adds a simple utility for fetching dependencies (*.py) and data files (*.csv) from a GitHub repository. The defaults are set for use with QuantEcon.notebooks.

Example

from quantecon import fetch_nb_dependencies
fetch_nb_dependencies(["Wald_Friedman_utils.py"])

but can be used with other repositories or branches etc.

#-Remote Structure-#
REPO = "https://github.com/QuantEcon/QuantEcon.notebooks"
RAW = "raw"
BRANCH = "master"
DEPS = "dependencies"          #Hard Coded Dependencies Folder on QuantEcon.notebooks

def fetch_nb_dependencies(files, repo=REPO, raw=RAW, branch=BRANCH, deps=DEPS, verbose=True):
    """
    Retrieve raw files from QuantEcon.notebooks Github repo

    Parameters
    ----------
    file_list   list or dict
                A list of files to specify a collection of filenames
                A dict of dir : list(files) to specify a directory
    repo        str, optional(default=REPO)
    branch      str, optional(default=BRANCH)
    deps        str, optional(default=DEPS)
    verbose     bool, optional(default=True)

    TODO
    ----
    1. Should we update this to allow people to specify their own folders on a different GitHub repo?

    """

This will download the file from GitHub (QuantEcon.notebooks/master/dependencies/) directly - allowing a notebook to be run anywhere. This can also be done with data files etc.