Improve memory management through more suitable allocators?

[ktnr]

https://github.com/r-lyeh-archived/ltalloc seems to work great. Observed runtime improvements in parallel mode with SolveParallelTaskflow() of up to 40%.

I do not yet have a good understanding of the suitability of this allocator, other than it states that it is suited for multi-threaded purposes. Is it similar to pool allocators? Might explicit pool allocators be more useful? Need to study the wiki.

Caution: Need to further evaluate the limitations for usage with Windows. By including the source files the operator new is globally overriden. This shouldn't affect precompiled dependencies. But it might have an effect on all projects that include this repo, and therefore also ltalloc.cc, as a submodule.