implement new iterator for trie_multiset and trie_multimap
test travis again
test travis, putting all command into jamfile
simple test of multiset, to be continue
add lower_bound, upper_bound and equal_range
add reverse_iterator, but not finished yet
reverse_iterator work well now, trie_multimap will be next target.
travis again
Update .travis.yml
Update .travis.yml
resolve the error of double free, it turned out that I call detroy()
twice in trie container
no more double free
Merge branch 'new_iter' of https://github.com/ithlony/Boost.Trie into new_iter

Conflicts:
	.travis.yml
no double free and will build pass on travis
separate each implementations,
add trie_multimap
close to complete a usable version
complete the functions of trie_containers
correct some mistakes in code that Antony pointed out
add two member to trie_node, in order to optimize the efficiency of
begin(), rbegin(), find_prefix() : from O(depth of tree) to O(1)
correct the wrong implementation of equal_range
refine the implementation of reverse_iterator, so that it complies to
the reverse_iterators of stl containers.
refine some little mistakes, begin trying to make the container of set with 'void' value type