Generalize the layer structure to support multiple parent dirs

The idea is to place all XD-build layers in build/, and possibly other
types of XD-embedded layers will live in other manifest subdirs.

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
Add custom TestCase class for unittest simplification

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
Cleanup unittest code

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
Rewrite manifest handling

* Use Windows INI file syntax in .xd file (closes #10)
* Use standard Python repository structure in layers (closes #8)
* Layer ordering support (closes #9)

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
Fix error handling of adding bad and incomplete layer commands

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
Unittest coverage completion

With this commit, we should reach 100% branch and statement coverage.
Let us try to keep it there.

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
Merge pull request #13 from esben/master

Features for milestone 0.1 and full unittest coverage