Issue 75: Add support for sorting Methods by priority

[fohrloop]

Add: get_prioritized_methods

Take an unordered list of Methods and sort them by priority using the priority_order and automatic ordering. The priority_order is used to define groups of priority (sets of methods). The automatic ordering part is used to order the methods within each priority group. In particular, all methods supported by the current platform are placed first, and all supported methods are then ordered alphabetically (ignoring case).

Example

Assuming: Current platform is Linux.

  >>> methods = [LinuxA, LinuxB, LinuxC, MultiPlatformA, WindowsA]
  >>> get_prioritized_methods(
  >>>    methods,
  >>>    priority_order=[{"WinA", "LinuxB"}, "*"],
  >>> )
  [LinuxB, WindowsA, LinuxA, LinuxC, MultiPlatformA]

Explanation:

WindowsA and LinuxB were given high priority, but since the current platform is Linux, LinuxB was prioritized to be before WindowsA.

The asterisk ('*') is converted to a set of rest of the methods: {"LinuxA", "LinuxC", "MultiPlatformA"}, and those are then
automatically ordered. As all of them support Linux, the result is just the methods sorted alphabetically. The asterisk in the end is optional; it is added to the end of priority_order if missing.