Remove memory.hpp's dependency on algorithm.hpp

[jrassi]

MSVC 2015 Update 3 chokes on compiling algorithm.hpp. memory.hpp doesn't use any functionality from algorithm.hpp, and removing this unnecessary dependency allows for a successful build of the former with this compiler.

[CLAassistant]

All committers have signed the CLA.

[bruxisma]

Hi! I can't merge this because of the failing build unfortunately, but once it's been fixed I'll merge it in. :)