longest_consecutive: Calculate the longest consecutive giving streak
In crazybilly/fundRaising: Functions for Fundraising Analytics

calculates the longest consecutive giving streak given giving details for constituents containing a fiscal year field

1	longest_consecutive(data, ids, fys, fy_range = NA, mode = "append")

`data`	a data frame with donor ids and the fiscal year of gifts
`ids`	an unquoted column name that contains the constituent IDs
`fys`	an unquote column name that contains the fiscal year for gifts. If not present, run fy() or fy2().
`fy_range`	the maximum consecutive giving streak to try to find. By default, this uses the maximum range given the fiscal years provided.
`mode`	options for the output mode. By default, "append" creates a new data frame with all provided columns and the consecutive giving years column. There are two other options. "just_consecutive" will provide a table of IDs and values representing the longest consecutive giving streak. "summary" provides a count of donors for every consecutive giving value.