loadStrings fix

loadStrings was returning an empty array ('ret'), before the array gets
populated with strings. So I deleted 'return ret' and put the array
'ret' into the callback function once it's populated. Now it's working
for me, hopefully for others too!
Effectively a rewrite/refactor of PImage. PImage's are now backed by a (non-rendered) canvas. Greater coverage of the PImage api.

PImages now use a backing canvas as their primary image representation, This change allows for more flexible manipulation of PImages,
and most of the PImage api is now implemented. Organizationally, the global drawing functions that handle drawing images were also
moved to the image.js file. The filter operation is still not implemented, and the mask function is not complete as per the processing's
original spec (though it supports similar functionality). The save functionality also does not support naming the downloaded file and probably
bears articulating out how we want this to work in the context of the web. It also only supports jpg and png formats.

One thing that has been removed at the moment is preloadImage(). I couldn't quite figure out how that was supposed to work
or if we want to keep it around.

I've added some examples in examples/pimage, they appear part way between a test suite and a set of user facing examples and could
probably be cleaned up in future.
Pass updated jshint validation.
Merge branch 'master' of github.com:therewasaguy/p5.js
merge pr
ran grunt, updating dist
fixing link to loop reference
fixing link to array access reference
adding createCanvas to API page
adding risdf13 examples 0-4
adding risdf13 examples 5-9
committing examples with tab spaces
cleaning up risdf13 examples so far
adding risdf13 examples 10-13
adding risdf13 examples 14-19
editing/adding instantiation examples
merging pimage
Merge branch 'master' of github.com:lmccart/p5.js
adding displayWidth and height and corresponding tests #106
fixing displaywidth better