Major rework of codebase

- Get rid of 'core' and move CLI to cmd/gas directory
- Migrate (most) tests to use Ginkgo and testutils framework
- GAS now expects package to reside in $GOPATH
- GAS now can resolve dependencies for better type checking (if package
  on GOPATH)
- Simplified public API

resolve.go

@@ -17,6 +17,7 @@ package gas
 import "go/ast"
 
 func resolveIdent(n *ast.Ident, c *Context) bool {
+
 	if n.Obj == nil || n.Obj.Kind != ast.Var {
 		return true
 	}