docs: Fix a few typos

[timgates42]

There are small typos in:

• doc/index.rst
• stream.py

Fixes:

• Should read represented rather than respresented.
• Should read further rather than futher.
• Should read first rather than firts.
• Should read available rather than avaiable.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md