Create Line Items script, line item struct.

Updated URLS for bad create line item.

Added account_exists function, takes username and account to check as
parameters. returns 1 or 0.

Defined lineitem struct, considering refactoring parameters to create
line item to take a single one of those as well as user and account.

Added error document for creating a line item

Added JS to append items to the table for the line items, though the
read lineitems script isn't done yet.

Created create-lineitem cgi script.