Rename SharedMemory* types to Shm*

[yellowhatter]

Describe the release item

In order to shorten type names as we did with ZSliceShm -> ZShm, I propose to do SharedMemory* -> Shm* renaming.

[yellowhatter]

@Mallets what would you say?

[Mallets]

I think it's ok to rename it to a shorter name. shm is already an established short version of shared memory.

[Mallets]

Closed by #1095