* Implemented git_diff_index_to_tree
* Reworked git_diff_options structure to handle more options
* Made most of the options in git_diff_options actually work
* Reorganized code a bit to remove some redundancy
* Added option parsing to examples/diff.c to test most options
This fixes several bugs, updates tests and docs, eliminates the
FILE* assumption in favor of printing callbacks for the diff patch
formatter helpers, and adds a "diff" example function that can
perform a diff from the command line.
This reworks the diff API to separate the steps of producing
a diff descriptions from formatting the diff. This will allow
us to share diff output code with the various diff creation
scenarios and will allow us to implement rename detection as
an optional pass that can be run on a diff list.
This gets the basic plumbing in place for git_diff_blob.
There is a known issue where additional parameters like
the number of lines of context to display on the diff
are not working correctly (which leads one of the new
unit tests to fail).
