Malloc wrapper + Panic function

I wrote a wrapper for `malloc` to do error handling, as described in issue #18.
There is also an implementation of a function to report critical failures.
`panic` is defined as a pointer to be able to replace it with a test double when we need it.

Those wrappers are not feature-complete yet but they are already usable and I will add features in other PR.
Features I would like to see : 

* Find a way to make `malloc` fail to test if the code properly recovers.
* Add a location (file + line) information to `panic` message.