Specify own RedisGears allocator.

[iddm]

Uses the new API of the redismodule crate to set custom global allocator.

[iddm]

@MeirShpilraien This uses the new API in the redismodule macro to set the global allocator by the implementor itself, so as to be able to fully control it. The code for the changes in redismodule -rs is in this PR: RedisLabsModules/redismodule-rs#307

[MeirShpilraien]

@vityafx This will basically create 2 allocators right? One for the core and one for plugins. I like this Idea but maybe we can take it one step forward and create an allocator per engine. It will give us more flexibility to show more per engine specific memory stats in the future. WDYT?

[iddm]

@vityafx This will basically create 2 allocators right? One for the core and one for plugins. I like this Idea but maybe we can take it one step forward and create an allocator per engine. It will give us more flexibility to show more per engine specific memory stats in the future. WDYT?

I apologise, but I think I should ask for an example to avoid confusion. Can you please add more colours to what you said?