xgbgen: process <doc> elements

Most of XCB documentation now ends up in Go sources,
although the end result is of mixed quality.

nexgb/xgbgen/context.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log"
 	"sort"
+	"strings"
 )
 
 // Context represents the protocol we're converting to Go, and a writer
@@ -34,6 +35,13 @@ func (c *Context) Put(format string, v ...interface{}) {
 	}
 }
 
+// PutComment writes each line of comment commented out to 'out'.
+func (c *Context) PutComment(comment string) {
+	for _, line := range strings.Split(comment, "\n") {
+		c.Putln("// %s", line)
+	}
+}
+
 // Morph is the big daddy of them all. It takes in an XML byte slice,
 // parse it, transforms the XML types into more usable types,
 // and writes Go code to the 'out' buffer.