Raise if not enough bind values are passed to a raw sql statement

[jhollinger]

Raises OccamsRecord::MissingBindValuesError if not enough bind values are passed in. #14

res = OccamsRecord.
  sql("SELECT * FROM widgets WHERE user_id = :user_id AND name = :name AND age = :age", {user_id: 5}).
  run

# OccamsRecord::MissingBindValuesError: Missing binds (name, age) in SELECT * FROM widgets WHERE user_id = %{user_id} AND name = %{name} AND age = %{age}

Positional binds will show the number of missing binds:

res = OccamsRecord.
  sql("SELECT * FROM widgets WHERE user_id = ? AND name = ? AND age = ?", [5]).
  run

# OccamsRecord::MissingBindValuesError: Missing binds (2) in SELECT * FROM widgets WHERE user_id = %s AND name = %s AND age = %s