Move a bunch of code that isn't specific to dms elsewhere

[anacrolix]

I made a lot of Python-like stuff while creating dms that really just clutters the code base. Stuff like rrcache, queue, futures and others aren't DMS specific and should be moved elsewhere, or rejigged using now-improved knowledge of Go idioms.

[anacrolix]

rrcache is the only one left. It's pretty specific to dms.

[Adirelle]

Note there is a lot of fine go libraries out there that could be used. https://github.com/avelino/awesome-go/blob/master/README.md lists a lot of them.