Implements simple embedding of images.

A new key `C-c C-i` is added to the markdown mode that allows people
to embed images into the blog post. At the end of the editing session,
the newly linked to images are moved to a hyde-images-dir directory.

Files modified:
hyde.el
- Adds some code to make sure that the hyde-home variable is passed to
  the markdown mode

hyde-md.el
- Adds the C-c C-i binding to embed images.
- Adds a function to extract images from the buffer.
- Adds a function to move the extracted images into hyde-images-dir.
- Calls this function when editing is done.
Expands file names before inserting them into the buffer.
Change order in which image rewriting functions are called.
Filter assets that need to be added into the local directory.
Use relative rather than absolute path to save images
Saves files after assets rewritten
Passes hyde-home to markdown buffer even when creating a new post
Commit assets along with post
Fixes hyde-get-post-assets to generate complete list of assets
Automatically commit when post edited
Creates image directories at the main entry point.
Use VC rename instead of just mv
Use buffer name rather than article title while committing
Don't run add if empty file list given.
Don't switch buffers while moving assets.
Automatically commit after promoting.
Change location of published asset directory.
Abort if .hyde.el not found.
Updates README for latest release
Merge branch 'auto-commit'

Conflicts:
	hyde-md.el