Support Python 3

[gmmeyer]

What does this PR do?

This makes Lighthttpd support Python 3.

The changes are largely small string handling issues, nothing major.

Motivation

🐍 3️⃣ 🚂

Review checklist

• PR has a meaningful title or PR has the no-changelog label attached
• Feature or bugfix has tests
• Git history is clean
• If PR impacts documentation, docs team has been notified or an issue has been opened on the documentation repo
• If PR adds a configuration option, it has been added to the configuration file.

Additional Notes

Anything else we should know when reviewing?

[codecov-io]

Codecov Report

Merging #2834 into master will decrease coverage by 3.53%.
The diff coverage is 80%.

@@            Coverage Diff            @@
##           master   #2834      +/-   ##
=========================================
- Coverage   84.73%   81.2%   -3.54%     
=========================================
  Files         662       4     -658     
  Lines       37615     133   -37482     
  Branches     4508      17    -4491     
=========================================
- Hits        31873     108   -31765     
+ Misses       4427      15    -4412     
+ Partials     1315      10    -1305