Add DocumentBuilder type

DocumentBuilder uses the builder pattern and Gemini's line-type specification
to pragmatically build gemini files line-by-line.

document.go

@@ -0,0 +1,78 @@
+package gemini
+
+// DocumentBuilder allows programatic document creation using the builder pattern.
+//
+// Example:
+// ```
+// document := NewDocumentBuilder()
+// document.AddH1Header("Hello world!")
+// document.AddLine("Reasons to use this builder:")
+// document.AddBullet("It's easy to use.")
+// document.AddBullet("it's easy to grok the code!")
+// document.AddLink("/about", "click here for more!")
+//
+// responseWriter.Write(document.Build())
+// ```
+type DocumentBuilder struct {
+    body string
+}
+
+// Instantiate a new DocumentBuilder.
+func NewDocumentBuilder() DocumentBuilder {
+    return DocumentBuilder{}
+}
+
+// Add a new line to the document. Adds a newline to the end of the line if none is present.
+func (self *DocumentBuilder) AddLine(line string) {
+    // Insure lines are always newline terminated
+    if len(line) == 0 || line[len(line) - 1] != '\n' {
+        line += "\n"
+    }
+
+    self.body += line
+}
+
+// Add an H1 (#) header line to the document.
+func (self *DocumentBuilder) AddH1Header(header string) {
+    self.AddLine("# " + header)
+}
+
+// Add an H2 (##) header line to the document.
+func (self *DocumentBuilder) AddH2Header(header string) {
+    self.AddLine("## " + header)
+}
+
+// Add an H3 (###) header line to the document.
+func (self *DocumentBuilder) AddH3Header(header string) {
+    self.AddLine("### " + header)
+}
+
+// Add a quote line to the document.
+func (self *DocumentBuilder) AddQuote(header string) {
+    self.AddLine("> " + header)
+}
+
+// Add an unordered list item to the document.
+func (self *DocumentBuilder) AddBullet(header string) {
+    self.AddLine("* " + header)
+}
+
+// Add a toggle formatting line to the document.
+func (self *DocumentBuilder) ToggleFormatting() {
+    self.AddLine("```")
+}
+
+// Add an aliased link line to the document.
+func (self *DocumentBuilder) AddLink(url string, title string) {
+    self.AddLine("=> " + url + "\t" + title)
+}
+
+// Add a link line to the document.
+func (self *DocumentBuilder) AddRawLink(url string) {
+    self.AddLine("=> " + url)
+}
+
+// Build the document into a serialized byte slice.
+func (self *DocumentBuilder) Build() []byte {
+    return []byte(self.body)
+}