Improve some package upgrade related messages.
Update change log.
Cache the results for upgrade suggestions.

The same results are not reused for one day instead of querying the registry every time. Note that this already used to be the case some time ago.
Fix possible range violation error when accessing the upgrade cache.
Merge pull request #367 from Geod24/fix-singlefile

Fix single file compilation for GDC.
Missing format() function.
Update link to Build Status
Merge pull request #369 from Geod24/fix-readme

[Trivial] Update link to Build Status
Merge pull request #368 from p0nce/master

Missing format() function.
Don't try to reinstall (remove) unmanaged branch based dependencies.
Don't print possible upgrades of the root package.
Fix lookup of sub packages from within sub packages of the same package. Fixes #357.

When the root package was a sub package, any reference to another sub package was looked up relative to the root (sub) package instead of its base package.
Add .def files to the list of source file types to pass to the linker.
Added unittest for basic usage cases.
Skip testing dynamic library until they are working
Merge pull request #371 from Geod24/moar-unittest

Create tests for basic dub usage + test with DMD 2.065.0 + LDC + GDC
Make it compile on raspi