Bugs Fixed

• gohcl: Fix panic when decoding into type containing value slices. (#335)
• hclsyntax: The unusual expression null[*] was previously always returning an unknown value, even though the rules for [*] normally call for it to return an empty tuple when applied to a null. As well as being a surprising result, it was particularly problematic because it violated the rule that a calling application may assume that an expression result will always be known unless the application itself introduces unknown values via the evaluation context. null[*] will now produce an empty tuple. (#416)
• hclsyntax: Fix panic when traversing a list, tuple, or map with cty "marks" (#424)