This cleans up make_repo.py a bit, using file extensions to determine
file type.
This also loosens the testing repo generation, as the existing
test required matching a predifed expected output which had to be
updated on every change (essentially making it a moot test, as the
reference output was obtained from the functions output).
The new test just checks if the output has the same number of packages
as the input dir has addons.
Tips on how best to test these sorts of "higher level" functions (if at
all) would be welcome :)
Moved repo.json generation to make_repo.py
Package/addon parsing is getting a bit messy, this can be
cleaned up when we have a clearer idea of what a package is.
For now just make it work.
