Now, if ANOTHER_MEMCHECK_QUIET environment variable is defined, do not
print output when malloc/calloc/free is called.
Minor refactoring: remove unused constexpr declarations in header.
Bump version to 2.2 .
Update Changelog.md .
Internally use doubly-linked list instead of singly-linked list. Also
minor fixes related to changing use to doubly-linked list.
Removed unnecessary comments.
Move list add/remove code to designated functions.
