mar_scrape

Scraping monthly activity returns data from NHS England

first functions added:

find_excels_MAR - which finds all .xls sheets on the NHS England Monthly Activity Return site.

get_main_MAR - which takes the output of find_excels_MAR and returns the main 'timeseries'. This is updated monthly.

Things to do:

_dl files:

• test commissioner/provider versions, should we allow both?
• add years to download
• need some verification mechanism to ensure what is downloaded is what is expected

_cl files:

• everything