vlib: use new filename format

vlib/strings/builder.js.v

@@ -0,0 +1,51 @@
+// Copyright (c) 2019-2020 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+
+module strings
+
+pub struct Builder {
+mut:
+	buf []byte
+pub mut:
+	len int
+	initial_size int = 1
+}
+
+pub fn new_builder(initial_size int) Builder {
+	return Builder {
+		buf: make(0, initial_size, sizeof(byte))
+		initial_size: initial_size
+	}
+}
+
+pub fn (b mut Builder) write_b(data byte) {
+	b.buf << data
+	b.len++
+}
+
+pub fn (b mut Builder) write(s string) {
+	b.buf.push_many(s.str, s.len)
+	//b.buf << []byte(s)  // TODO
+	b.len += s.len
+}
+
+pub fn (b mut Builder) writeln(s string) {
+	b.buf.push_many(s.str, s.len)
+	//b.buf << []byte(s)  // TODO
+	b.buf << `\n`
+	b.len += s.len + 1
+}
+
+pub fn (b Builder) str() string {
+	return string(b.buf, b.len)
+}
+
+pub fn (b mut Builder) cut(n int) {
+	b.len -= n
+}
+
+pub fn (b mut Builder) free() {
+	b.buf = make(0, b.initial_size, 1)
+	b.len = 0
+}