Fix #41 and #42

[pavel-kirienko]

Fixes #41 Fixes #42

Now, in case of an accidental misuse like in https://forum.uavcan.org/t/dsdl-compilation-error/904/2, the error message will contain a helpful suggestion:

/home/pavel/test/demo/dsdl/my_namespace/Trajectory.1.0.uavcan:1: Data type my_namespace.PointXY.1.0 could not be found in the following root namespaces: {'dsdl'}.  Did you mean to use the directory '/home/pavel/test/demo/dsdl/my_namespace' instead of '/home/pavel/test/demo/dsdl'?

[coveralls]

Pull Request Test Coverage Report for Build 34691594

• 28 of 28 (100.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 34690396:	0.0%
Covered Lines:	2964
Relevant Lines:	2964

---

💛 - Coveralls