- added find() (like has(), but returns list of all occurrences)

- added find() (like has(), but returns list of all occurrences)
- added lst::sort() and lst::unique()
- status_flags::expanded is only taken into account when no expand options
  are specified. This makes it possible to re-expand with other options.
- added expand_options::expand_function_args
- collect(foo, {}) doesn't crash any more
- introduced match_same_type() method which is slightly similar to
  is_equal_same_type() but doesn't check subexpressions. Fixed a number of
  match() bugs with this (e.g. a==b matched a!=b, and matrices with different
  dimensions but the same number of elements could match). Only container
  classes with additional member variables that have to be equal for a match
  need to implement match_same_type().