EPUB Reader: Removed incorrectly set reader flag
Shared: Added collapseFilePath function

This function removes intermediate "." and ".." from a path.
Added tests for collapseFilePath
EPUB Reader: Use collapseFilePath
EPUB Reader: Fixed regressions in image extraction

Before the images were relative to the position of the package file. The
collapse function changed this so that they were then absolute in the
archive but the fetchImages function wasn't updated to recognise this.
EPUB Reader: Improved robustness of image extraction

We now maintain the invariant that when fetchImages is called,
all images have absolute paths.

This patch fixes several bugs relating to this as there are three places
where images can be introduced.
  (1) During the HTML parse
  (2) As spine elements
  (3) As a cover image

For (1), the paths are corrected by the transformation renameImages
For (2) and (3), we need to append the "root" to the path we parse from the
spine
Merge branch 'newbranch' of https://github.com/mpickering/pandoc into mpickering-newbranch

Conflicts:
	src/Text/Pandoc/Readers/EPUB.hs
Updated changelog.