add_generic_positions_constraint: Add custom position constraints
In zamorarr/coach: Lineup optimization for daily fantasy sports

Add custom position constraints

1	add_generic_positions_constraint(model, data, constraints)

`model`	a coach model
`data`	data frame with fpts projections
`constraints`	a named list with constraints. Flex or Wildcard positions should be named with a / between positions. See examples.

## Not run: 
data <- read_dk("yourfilenamehere.csv")
constraints <- list("QB" = 1, "RB" = 2, "WR" = 3, "TE" = 1, "RB/WR/TE" = 1, "DST" = 1)
model <- model_generic(data, total_salary = 50E3, roster_size = 9, max_from_team = 4)
model <- add_generic_positions_constraint(model, data, constraints)

## End(Not run)