String * number should be commutative
Added `join` function

Signed-off-by: Nicolas Williams <nico@cryptonector.com>
Document `index` and `rindex` (#389)
Remove reference to `getpath` from docs
Improve `index` and `rindex` examples
Add `indices(s)`, improve `index(s)`, `rindex(s)`

Now these deal with arrays as input and `s` being an array or a scalar.
Add test of `indices` with short input