Support Windows

[umanwizard]

Cc @roblabla

[roblabla]

Yeah I'm working on this. It turned out to require changes across the stack:

• In jemalloc itself:
  • I had to add support for MSVC backtracking so the profiling feature worked: JustRustThings/jemalloc@9e2edd7
  • I had to change how weak symbols are handled for malloc_conf so it supports MSVC toolchains: JustRustThings/jemalloc@783dc01
• In jemallocator, I had to fix a lot of errors related to windows support in the build system: Fix windows support tikv/jemallocator#99
• And in this repo, I need to add support for getting windows mappings.

I'm slowly working towards getting everything in a working state, before I start sending pull requests upstream.

[umanwizard]

That will be really awesome if you can get it working! Let me know if you need any help on this repo's side.