Add jemalloc\tcmalloc allocators

[anovoselcev]

This patch add jemalloc and tcmalloc allocators support. I've investigated that it helps to reach better performance and memory consumption in parallel search context.

[zayenz]

Thanks for this proposal. I am, however, unsure if it is the right way to go, at least right now.

Personally, I've used mimalloc when using Gecode in a multi-threaded setting on a Mac, as it gives a significant performance boost. However, as Gecode is often used as a library that is built into another system, hopefully the allocator used is coming from outside of Gecode anyway.