Rename Dev Guide chapters based on chapter titles.

Hi Rich,
I wanted to rename these to map to the chapter titles, as done with the User Guide Markdown files. I see where it will be easier for contributors to find them. 

I tried to start each filename with the first word of the chapter title and include the topical item (e.g., opensocial gadget) in the file name. In some cases, I omitted middle words to keep the filename from being too long.

Since I used 'git mv source dest', the Git logs are carried over to each newly named file.

Thanks,
Jim