Support for large files upload

[przemekperon]

Large files (5GB or more) upload works in different way than standard file upload:
https://www.backblaze.com/b2/docs/large_files.html

This pull request implements large files support for files larger than 3GB.

[przemekperon]

Also added upload resume for large files (resume after "is too busy" error).

@cwhite92 Any chances of merging this into the repository?

PS: Travis failed because of HHVM incompatibility and not because of my commits.

[reinierkors]

I still seem to get errors when using your branch.

B2Exception: Received error from B2: c001_v0001100_t0001 is too busy

and

B2Exception: Received error from B2: Not enough members for write of {errorcode}: class java.net.SocketException - Connection reset