Implementing generic parser plugins and documentation

This constitutes a large change in how we will parse different data
formats going forward (for the plugins that support it)

This is working off @henrypfhu's changes.

plugins/parsers/influx/parser.go

@@ -0,0 +1,57 @@
+package influx
+
+import (
+	"bytes"
+	"fmt"
+
+	"github.com/influxdata/telegraf"
+
+	"github.com/influxdata/influxdb/models"
+)
+
+// InfluxParser is an object for Parsing incoming metrics.
+type InfluxParser struct {
+	// DefaultTags will be added to every parsed metric
+	DefaultTags map[string]string
+}
+
+// ParseMetrics returns a slice of Metrics from a text representation of a
+// metric (in line-protocol format)
+// with each metric separated by newlines. If any metrics fail to parse,
+// a non-nil error will be returned in addition to the metrics that parsed
+// successfully.
+func (p *InfluxParser) Parse(buf []byte) ([]telegraf.Metric, error) {
+	// parse even if the buffer begins with a newline
+	buf = bytes.TrimPrefix(buf, []byte("\n"))
+	points, err := models.ParsePoints(buf)
+	metrics := make([]telegraf.Metric, len(points))
+	for i, point := range points {
+		tags := point.Tags()
+		for k, v := range p.DefaultTags {
+			// Only set tags not in parsed metric
+			if _, ok := tags[k]; !ok {
+				tags[k] = v
+			}
+		}
+		// Ignore error here because it's impossible that a model.Point
+		// wouldn't parse into client.Point properly
+		metrics[i], _ = telegraf.NewMetric(point.Name(), tags,
+			point.Fields(), point.Time())
+	}
+	return metrics, err
+}
+
+func (p *InfluxParser) ParseLine(line string) (telegraf.Metric, error) {
+	metrics, err := p.Parse([]byte(line + "\n"))
+
+	if err != nil {
+		return nil, err
+	}
+
+	if len(metrics) < 1 {
+		return nil, fmt.Errorf(
+			"Can not parse the line: %s, for data format: influx ", line)
+	}
+
+	return metrics[0], nil
+}