Add function to get SRS from epsg.io

The function queries http://epsg.io for definition of a Spatial
Reference System by a European Petrol Survey Group Code and returns it
as text in a specified format.
Rename function srs_str_by_epsg to epsg

srs_str_by_epsg is now called epsg and the docstring contains correct
formats.
Add intro video link to readme
Increase version number
Merge pull request #13 from NERC-CEH/develop

Merge Develop after epsg function