Created base for parser

The parser now handles file opening and invokes the lexer.

parser/tree.go

@@ -0,0 +1,8 @@
+package parser
+
+// SyntaxTree represents an abstract syntax tree. It covers an entire module. It
+// can be expected to be syntactically correct, but it might not be semantically
+// correct (because it has not been analyzed yet.)
+type SyntaxTree struct {
+	
+}