add build status and API docs to README

README.md

@@ -1,15 +1,40 @@
 # xm.js
 
+[![Build Status](https://travis-ci.org/a1k0n/jsxm.svg?branch=master)](https://travis-ci.org/a1k0n/jsxm)
+
 FastTracker 2 .XM player, written for fun.
 
 [Demo](http://www.a1k0n.net/code/jsxm/)
 
-By default it plays "my dirty old kamel" by Alexander Bulér aka
-[Zalza](http://zalza.bandcamp.com/). I love this tune, and wrote this code just
-to play it. It can also load some other tunes hosted on my website with a file
-picker, and it should play just about any .XM file now if checked out and run
-locally.
+There is an XM player and a visualizer which are separate components. The
+player API looks like this:
 
-It is fairly feature-complete, but is missing a bunch of effects.
+ - `XMPlayer.initAudio` -> starts up audio context; it's available as
+   `XMPlayer.audioctx`
+ - `XMPlayer.loadXM(ArrayBuffer)` -> returns `true` if loaded, otherwise
+   barfs randomly
+ - `XMPlayer.playXM()` -> starts playing
+ - `XMPlayer.pauseXM()` -> obvious
+ - `XMPlayer.stopXM()` -> obvious; call this before loading a new one
+
+Loading trackview.js is optional; without it, the player won't do any
+visualizations. Or, you can override the following to get callbacks:
+
+ - `XMView.pushEvent(e)` -> push an audio event onto the queue. Called
+   once per tick (about 50Hz, controlled by song). `e` contains fields:
+   - `t` - audio timestamp
+   - `vu` - Float32Array of RMS power (volume) for each channel
+   - `scopes` - [Float32Array] of oscilloscope data, one array per
+     channel; `XMView.scope_width` contains # of samples to produce here
+   - `songpos` - position in the song (# patterns played)
+   - `pat` - pattern number currently playing
+   - `row` - row within pattern
+ - `XMView.pause()` - pause visualization
+ - `XMView.stop()` - stop/reset visualization
+
+The code which defines what the buttons do and downloads songs and so
+forth is in `shell.js`.
+
+The player is fairly feature-complete, but is missing a bunch of effects.
 
 MIT license.