Ensure mutable sequence implementations include all appropriate methods and operators

[simpleigh]

Ensure we're following the following guidelines in the Python language specification:

Mutable sequences should provide methods append(), count(), index(), extend(), insert(), pop(), remove(), reverse() and sort(), like Python standard list objects. Finally, sequence types should implement addition (meaning concatenation) and multiplication (meaning repetition) by defining the methods add(), radd(), iadd(), mul(), rmul() and imul() described below; they should not define other numerical operators

Are there appropriate methods or operators that we ought to implement on types within the library?