Update documentation
Update documentation
Update documentation and add menu item for export

Altered items:
simple-call-tree-mode
Add new sort command: sort by number of children

Altered items:
simple-call-tree-default-sort-method, simple-call-tree-mode,
simple-call-tree-build-tree, simple-call-tree-sort-by-num-children,
simple-call-tree-sort-alphabetically