add interface for SchematicValueVisitor
schematic test cases: exceptions for getters
schematic test cases: exceptions for type adders
schematic test cases: exceptions for node/connection adders and getters
schematic test cases: exceptions for constraints
reorganize the order of test cases to keep similar checks together
schematic test cases: explicit tests for all getters

because nontrivially unreachable cases can't be excluded from coverage,
this is about as comprehensive as the tests can get for Schematic
Merge pull request #11 from maxqchen/master

serialization - types only
add very simple frontend and backend service interfaces
Merge pull request #12 from mtrberzi/schematic-value-visitor

Add interface for SchematicValueVisitor
Merge branch 'master' into schematic-tests
Merge pull request #13 from mtrberzi/schematic-tests

Test cases for Schematic
add invocation function to interface
checkstyle tho
version bump: 0.2.0
Merge branch 'master' into service-interface

Conflicts:
	build.gradle
fix accidental inclusion of merge line
Merge pull request #15 from mtrberzi/service-interface

add very simple frontend and backend service interfaces
add type inheritance to port, node, connection, constraint
version bump: 0.3.0