Dynamic graphs for counters and gauges

I've been busy implementing some of the feature requests I've gotten the last few days. Today I'm releasing the result as ekg v0.3. Here's what's new:

Counters and gauges

The old counter concept has been split up into two concepts: counters and gauges. Counters are monotonically increasing while gauges are not. An example of a counter would be requests served since program start and an example of a gauge would be the number of concurrent connections at a given point in time.

The counter/gauge distinction lets us do smarter things in the web interface. For example, given a counter called "iterations", we know that it ought to be graphed as iterations per second, instead of the raw value:

Graphing the raw value wouldn't be very interesting as it would result in a graph that just went straight up to the right.

Graphs for user-defined counters and gauges

The web interface now lets you dynamically add (and remove) graphs for user-defined counters and gauges. To add a graph, click on the little graph icon to the right of the counter or gauge name:

Reorganized REST API

The REST API has been reorganized to allow for finer-grained access to resources e.g. you can request all counters without also getting all gauges.

Server time instead of client time

In previous versions I used the client (i.e. browser) time when plotting graphs. This isn't a terribly good idea as network latency will skew the graphs. Version 0.3 uses the server time instead of client time to render graphs.

Usability improvements

I've also made a few minor usability improvements, such as adding column headers, improving number formatting, adding error messages, and reorganizing the user interface.