Added contribution and code style guidelines.

While Flot's codebase is currently a mish-mash of styles, we'd like to
move toward a unified style based on the jQuery core style guidelines.
Migration of existing code is scheduled for the 0.9 release.

CONTRIBUTING.md

+## Contributing to Flot ##
+
+We welcome all contributions, but these simple rules will greatly reduce the
+amount of work and time that it takes to process your pull request:
+
+ 1. Divide larger changes into a series of small, logical commits with
+	descriptive messages.
+
+ 2. Format your code according to the style guidelines below.
+
+ 3. Rebase against master, if necessary, before submitting your pull request.
+
+### Flot Style Guidelines ###
+
+Flot follows the [jQuery Core Style Guidelines](http://docs.jquery.com/JQuery_Core_Style_Guidelines),
+with the following minor changes:
+
+#### Comments ####
+
+Use // for all comments except the header at the top of a file or inline
+include.
+
+All // comment blocks should have an empty line above *and* below them. For
+example:
+
+```js
+	var a = 5;
+
+	// We're going to loop here
+	// TODO: Make this loop faster, better, stronger!
+
+	for ( var x = 0; x < 10; x++ ) {}
+```
+
+#### Wrapping ####
+
+Block comments should be wrapped at 80 characters.
+
+Code should attempt to wrap at 80 characters, but may run longer if wrapping
+would hurt readability more than having to scroll horizontally.  This is a
+judgement call made on a situational basis.
+
+Statements containing complex logic should not be wrapped arbitrarily if they
+do not exceed 80 characters. For example:
+
+```js
+	WRONG
+	if (a == 1 &&
+		b == 2 &&
+		c == 3) {}
+
+	CORRECT
+	if ( a == 1 && b == 2 && c == 3 ) {}
+```
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