targz support

[stuartpb]

This would make Pull Tool usable for Cloud9.

[stuartpb]

Classifying this as 2floc under the assumption that interfacing with an existing tgz library will be roughly as simple as interfacing with JSZip.

[stuartpb]

ugh, I just looked at https://github.com/stuartpb/targz.js/blob/master/gzip.js and it looks like the currently available code for this is hardcoded around XHR, so I'm going to need to do a bunch of hacking around it to add something that can take an already-fetched blob, eck eck eck

[stuartpb]

Luckily, I just found another browser JS TAR library, whose development started in August, that looks significantly more enlightened, so there may be life in this feature yet.

[stuartpb]

Yeah, I looked into this again, and I can use that uncompression library that JSZip uses (pako) to handle the gz side of things, then another untar library (this or this) to handle the untar bits