Doc cleanup and s/tiff/cr/ in error messages.

This library was forked from the tiff library, but is distinct.  The error
messages should indicate that to aid in debugging.

Removed one limitation in package doc, more tests were added in commit
a67a1ab62fb3eb9e699f85116ab4e24b639de04e
Merge pull request #2 from wathiede/doc-cleanup

Doc cleanup and s/tiff/cr/ in error messages.