fix antlr4 generated source output directory
simple driver for digital backends
currently using a test class to generate Schematics
this will be removed once support for JSON import is ready
Merge branch 'issue120-vhdl-codegen' into backend-invocation
Merge branch 'issue120-vhdl-codegen' into backend-invocation
Merge branch 'issue120-vhdl-codegen' into backend-invocation
WIP, testing code gen for registers
vhdl codegen tests for top-level I/O and non-existant output dirs
vhdl codegen tests for register signal declarations
vhdl codegen test for async reset
vhdl codegen runs design checks, CLI option to disable all checks
vhdl codegen: AND, OR, NOT
Merge branch 'master' into backend-invocation

Conflicts:
	build.gradle
	src/test/java/org/manifold/compiler/back/TestVHDLCodeGenerator.java
remove spurious debugging messages
allow digital backend to accept input from JSON file
checkstyle fixes tho
Merge branch 'master' into vhdl-codegen-tests

Conflicts:
	src/test/java/org/manifold/compiler/back/TestVHDLCodeGenerator.java
Enable type checking for attributes #80

Should this check if attributes are a subtype or equal?

Also, it seems like some types, such as NodeTypeValue, wouldn't make sense as
an Attribute.
Should the values in an Attribute be restricted to satisfy
isRuntimeKnowable() or isElaborationTimeKnowable?
Merge pull request #139 from mtrberzi/backend-invocation

Backend invocation
hotfix: changed constructor invocation for check
Merge pull request #147 from mtrberzi/hotfix-check

hotfix: changed constructor invocation for check