Implemented a basic API for SSA

src/ssa/Function.go

@@ -1,5 +1,13 @@
 package ssa
 
+// Function is a list of basic blocks.
 type Function struct {
 	Blocks []*Block
+}
+
+// AddBlock adds a new block to the function.
+func (f *Function) AddBlock() *Block {
+	block := &Block{}
+	f.Blocks = append(f.Blocks, block)
+	return block
 }