Compute unsealed sector CID syscall

[austinabell]

Summary of changes
Changes introduced in this pull request:

• Implements the compute_unsealed_sector_cid syscall in the runtime
  • Interfaces through the filecoin-proofs-api
• Updates commcid interface to take in references (was no need to move variables before, but assumed they wouldn't be needed after)

Dependent on #357 so I will remove other commits when that comes into mater and open this PR up

Reference issue to close (if applicable)

Closes
#303

Other information and links

[ec2]

Why the departure from our standard way of declaring dependencies?

[ec2]

Also, don't understand why we need to specify a version if we already specify a rev.

[austinabell]

just for safety, and the reason I used this format is just to make updating commit easier and more visible, I'll change to other format tho

[ec2]

Same as the comment in vm/Cargo.toml

[ec2]

let sum: u64 = pieces.iter().map(|p| p.size.0).sum();

Now sum doesn't have to be mut. Not an important change, but a fun one.

[ec2]

line 23 in vm/src/piece/mod.rs
pub fn validate(self) -> Result<(), &’static str> {
Can probably take a ref. I couldnt comment on that line so posting here

[austinabell]

line 23 in vm/src/piece/mod.rs
pub fn validate(self) -> Result<(), &’static str> {
Can probably take a ref. I couldnt comment on that line so posting here

Nah it's just a u64 so better to just move in. Pretty sure clippy warns on this