Replacing our Tus upload integration with TusPHP.

[erunion]

• Replace our Tus upload integration with https://github.com/ankitpokhrel/tus-php.
• Changes our PHP requirement from >=5.3.0 to >=7.1.0. Had to do this because tus-php requires 7.1+.
• Loading Psalm and setting it up to execute static analysis checks during the test process.

With these changes, I was able to upload video files that ranged from 13-793MB large. Since the default PHP memory limit is 128MB, we're uploading in 100MB chunks, so anything larger than what I've tested with should function just as well.

Since this is a breaking change, this'll be tagged released as v3.0.

Resolves #168

[Onebrownsound]

LGTM. Nice to see parity between the SDKs. One minor comment, but other than that gj!

[Onebrownsound]

This is okay for now, imo. But maybe mark this as a #TODO to export into it's own static function that takes in the path and returns all the necessary pieces, as a list or something. For testability and such.

[ghost]

I'm using PHP 7.2 and Vimeo 3.0 but I can't upload big files using tus approach (PATCH).
I receive a message like this: SSL_write() returned SYSCALL, errno = 32
I can complete the upload only if I use very small videos.