bashrc: add *.wiki to clean_whitespace extension list
unicode-characters: default to Python 3

You can still run this with Python 2 using e.g. `python2 $(which
unicode-characters.py)` but it's better to use Python 3's native Unicode
support where available.
update-home: handle empty source directories

Git won't store a completely empty directory…
.gitignore: skip Transifex .tx local config
Akamai Headers: httpie wrapper which prints diagnostic information