add feature to show a subset of graphs from a plugin on overview page
conf: disable overview_filter by default

It's good to have an example, but it's a bit confusing having it enabled by
default.
rewrite some code of added overview_filter feature

Use less variables, less code.
plugin: Add MD plugin
plugin/nut: collectd 5 compatibility + Add frequency graph
Merge pull request #5 from mce35/nut

plugin/nut: collectd 5 compatibility + Add frequency graph
import js directory from jsrrdgraph for client side graph rendering

Source: https://github.com/manuelluis/jsrrdgraph@276b880
type: stick to the rrdgraph time specification

Reference: http://rrdtool.mirror.graemef.net/doc/rrdfetch.en.html#IAT_STYLE_TIME_SPECIFICATION
move width/heigth from plugins to type __construct
jsrrdgraph: RrdGraph.js: fix undefined 2nd argument of RrdVdef function

This fixes this error:
> TypeError: Cannot call method 'indexOf' of undefined at new RrdVdef
integrate jsrrdgraph in CGP
.htaccess: enable gzip on rrd files
add support for graphing I/O using the negative X-axis
jsrrdgraph: RrdGraph.js: gprint: fix check for undefined format in case of vdef

The GPRINT of a VDEF doesn't have a CF. For example:
> "GPRINT:avg:LAST:%5.1lf%s Last"
> "GPRINT:tot:%5.1lf%s Total\l"

The format will be passed via the cf variable, so format is not defined. But it
didn't show up in the legend. Firebug showed variable format isn't undefined,
but an empty string in case of VDEF. So just check for falsy.
type/default: add missing initial variable definitions
add config option for showing smooth (curved) graphs
conf: set default collectd version to 5
update changelog to v0.4
remove dependency on mod_rewrite for rrd.php

Use $_SERVER['PATH_INFO'] instead.
update changelog to v0.4.1