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
Merge branch 'master' into vhdl-codegen-tests

Conflicts:
	src/test/java/org/manifold/compiler/back/TestVHDLCodeGenerator.java
Merge pull request #145 from mtrberzi/vhdl-codegen-tests

VHDL codegen tests