New documentation about gperftools guts

[Aliaksey Kandratsenka]

Hi. I've just uploaded a wiki page with some details about areas of non-trivial behavior or complexity in gperftools. See here: https://github.com/gperftools/gperftools/wiki/gperftools-tcmalloc-areas-of-complexity

I am about to make an RC cut for the upcoming 2.16 release. One area that changed quite a bit in this upcoming release is around TLS handling. Which is one of the areas I described in that wiki page.

Please, consider reviewing (and testing) both the wiki page and relevant code.