Implement piping.

Implements the API: /csv/head -n 20/html/?url=....

NO DOCUMENTATION OF APIS. Sad Face. 
Try this: 
http://localhost:5000/csv/head%20-n%2035/delete%201,2,3,4,5/grep%20LONDON/html?url=http://static.london.gov.uk/gla/expenditure/docs/2012-13-P12-250.csv
 
Also implements simplistic grep.
grep is case sensitive. 
NOTE: Adds underscore to requirements

refs #2
refs #13