add a standard library, and introduce formed imports (import std "myfile.pork")

ast/src/main/ast/pork.yml

@@ -110,6 +110,8 @@ types:
   ImportDeclaration:
     parent: Declaration
     values:
+    - name: form
+      type: Symbol?
     - name: path
       type: StringLiteral
   IntLiteral:

ast/src/main/kotlin/gay/pizza/pork/ast/ImportDeclaration.kt

@@ -6,22 +6,23 @@ import kotlinx.serialization.Serializable
 
 @Serializable
 @SerialName("importDeclaration")
-class ImportDeclaration(val path: StringLiteral) : Declaration() {
+class ImportDeclaration(val form: Symbol?, val path: StringLiteral) : Declaration() {
   override val type: NodeType = NodeType.ImportDeclaration
 
   override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
-    visitor.visitNodes(path)
+    visitor.visitNodes(form, path)
 
   override fun <T> visit(visitor: NodeVisitor<T>): T =
     visitor.visitImportDeclaration(this)
 
   override fun equals(other: Any?): Boolean {
     if (other !is ImportDeclaration) return false
-    return other.path == path
+    return other.form == form && other.path == path
   }
 
   override fun hashCode(): Int {
-    var result = path.hashCode()
+    var result = form.hashCode()
+    result = 31 * result + path.hashCode()
     result = 31 * result + type.hashCode()
     return result
   }