Avoids segfault by not freeing the internal structure handling memory
allocations. When the process ends, the OS should reclaim all memory,
even if it isn't free'd during process execution.
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.
