Log the Buildozer.spec delta

[Julian-O]

New feature suggestion:

In bug reports and support requests, we often ask for the Buildozer build logs, and also a copy of the Buildozer spec.

We don't need to ask for a copy of the environment variables, because they are automatically included in the log if the build fails.

My suggestion is to also include the Buildozer.spec in the logs.

But the Buildozer.spec tends to be a long document. It can be difficult to quickly see the few changes the user has made.

Therefore, I propose that what is logged is merely the differences - the default.spec should be loaded in as a ConfigParser instance, and Buildozer should iterate over the two instances looking for changes (modifications, deletions and additions) and just include those in the log.

For most projects, this list is likely to be short; if it isn't, that is likely to be pertinent.