Log Message:
libsass: updated to 3.6.4

3.6.4:
Fix parenthesization for selector schema and real parents
Add deprecation warning for global variable creation
Ensure correct output order of compound selectors
Handle loaded source code as shared objects
New custom memory allocator - disabled for now
Add back C-API getters for plugin paths
Fix abspath handling on windows without directory
Fix various edge case crashes
Fix segfault on directive ruleset
Fix heap-buffer-overflow in lexer
Fix stack-overflow in parser
Fix memory leak in parser
Fix memory leak in evaluation
Fix memory handling edge case
Fix some null pointer access crashes
Preparations for ongoing refactoring