docs: Fix a few typos

[timgates42]

There are small typos in:

• tlslite/init.py
• tlslite/extensions.py
• tlslite/messages.py
• tlslite/tlsconnection.py
• unit_tests/test_tlslite_extensions.py
• unit_tests/test_tlslite_messages.py

Fixes:

• Should read length rather than lenght.
• Should read successfully rather than succesfully.
• Should read element rather than elemnt.
• Should read element rather than elemnet.
• Should read programmer rather than programmmer.
• Should read networking rather than neworking.
• Should read instance rather than insance.
• Should read encoding rather than endoding.
• Should read convenience rather than convinience.
• Should read challenge rather than challange.
• Should read openpgp rather than opengpg.

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

[tomato42]

this repository is dead, I maintain an active fork at https://github.com/tlsfuzzer/tlslite-ng