v4.1.0

• Fixes memory leaks in ResultContext.filter method (native context was not getting deallocated after using the iterator)
• Bumps libuast version, which includes memory leak patches and a new iteration order: ChildrenOrder. Also ensures those iteration orders correspond to the ones present in libuast, lifting them from the native side.
• Adds managed context functionality:

# context owned by libuast
ctx = client.parse(filename)

# load to Python
ast = ctx.root.get()
# if we had a method to rename some nodes, for example
modified_dict = rename_variables(ast)

# context owned by Python
ctx = bblfsh.context(modified_dict)
... = ctx.filter("//uast:Identifier")